Formation of thin film capacitors

ABSTRACT

Thin layer capacitors are formed from a first flexible metal layer, a dielectric layer between about 0.03 and about 2 microns deposited thereon, and a second flexible metal layer deposited on the dielectric layer. The first flexible metal layer may either be a metal foil, such as a copper, aluminum, or nickel foil, or a metal layer deposited on a polymeric support sheet. Depositions of the layers is by or is facilitate by combustion chemical vapor deposition or controlled atmosphere chemical vapor deposition.

This a continuation-in-part of copending application Ser. No.09/198,285, filed on Nov. 23, 1998.

The present invention is directed to the formation of thin layercapacitors, preferably for printed circuitry, such thin layers beingcapable of being embedded within a printed circuit board. In particular,the invention is directed to forming thin layer capacitors from thinlayers of dielectric material which may be deposited by combustionchemical vapor deposition.

BACKGROUND OF THE INVENTION

Combustion chemical vapor deposition (“CCVD” ), a recently invented CVDtechnique, allows for open atmosphere deposition of thin films. The CCVDprocess offers several advantages over other thin-film technologies,including traditional CVD. The key advantage of CCVD is its ability todeposit films in the open atmosphere without any costly furnace, vacuum,or reaction chamber. As a result, the initial system capitalizationrequirement can be reduced up to 90% compared to a vacuum based system.Instead of a specialized environment, which is required by othertechnologies, a combustion flame provides the necessary environment forthe deposition of elemental constituents from solution, vapor, or gassources. The precursors are generally dissolved in a solvent that alsoacts as the combustible fuel. Depositions can be performed atatmospheric pressure and temperature within an exhaust hood, outdoors,or within a chamber for control of the surrounding gasses or pressure.

Because CCVD generally uses solutions, a significant advantage of thistechnology is that it allows rapid and simple changes in dopants andstoichiometries which eases deposition of complex films. The CCVDtechnique generally uses inexpensive, soluble precursors. In addition,precursor vapor pressures do not play a role in CCVD because thedissolution process provides the energy for the creation of thenecessary ionic constituents. By adjusting solution concentrations andconstituents, a wide range of stoichiometries can be deposited quicklyand easily. Additionally, the CCVD process allows both chemicalcomposition and physical structure of the deposited film to be tailoredto the requirements of the specific application.

Unlike conventional CVD, the CCVD process is not confined to anexpensive, inflexible, low-pressure reaction chamber. Therefore, thedeposition flame, or bank of flames, can be moved across the substrateto easily coat large and/or complex surface areas. Because the CCVDprocess is not limited to specialized environments, the user cancontinuously feed materials into the coating area without disruption,thereby permitting batch processing. Moreover, the user can limitdeposition to specific areas of a substrate by simply controlling thedwell time of the flame(s) on those areas. Finally, the CCVD technologygenerally uses halogen-free chemical precursors having significantlyreduced negative environmental impact.

Numerous materials have been deposited via CCVD technology with thecombustion of a premixed precursor solution as the sole heat source.This inexpensive and flexible film deposition technique permits broaduse of thin film technology. The CCVD process has much of the sameflexibility as thermal spraying, yet creates quality, conformal filmslike those associated with conventional CVD. With CCVD processing, adesired phase can be deposited in a few days and at relatively low cost.

A preferred embodiment of the CCVD process is described in detail inU.S. application Ser. No. 08/691,853 filed Aug. 2, 1996, the teachingsof which are incorporated herein by reference. In accordance with thatapplication, a CCVD produces vapor formed films, powders and nanophasecoatings from near-supercritical liquids and supercritical fluids.Preferably, a liquid or liquid-like solution fluid containing chemicalprecursor(s) is formed. The solution fluid is regulated to near or abovethe critical pressure and is then heated to near the supercriticaltemperature just prior to being released through a restriction or nozzlewhich results in a gas entrained very finely atomized or vaporizedsolution fluid. The solution fluid vapor is combusted to form a flame oris entered into a flame or electric torch plasma, and the precursor(s)react to the desired phase in the flame or plasma or on the substratesurface. Due to the high temperature of the plasma much of the precursorwill react prior to the substrate surface. A substrate is positionednear or in the flame or electric plasma, and a coating is deposited.Alternatively, the material formed can be collected as a nanophasepowder.

Very fine atomization, nebulization, vaporization or gasification isachieved using solution fluids near or above the critical pressure andnear the critical temperature. The dissolved chemical precursor(s) neednot have high vapor pressure, but high vapor pressure precursors canwork well or better than lower vapor pressure precursors. By heating thesolution fluid just prior to or at the end of the nozzle or restrictiontube (atomizing device), the available time for precursor chemicalreaction or dissolution prior to atomization is minimized. This methodcan be used to deposit coatings from various metalorganics and inorganicprecursors. The fluid solution solvent can be selected from any liquidor supercritical fluid in which the precursor(s) can form a solution.The liquid or fluid solvent by itself can consist of a mixture ofdifferent compounds.

A reduction in the supercritical temperature of the reagent containingfluid produces superior coatings. Many of these fluids are not stable asliquids at STP, and must be combined in a pressure cylinder or at a lowtemperature. To ease the formation of a liquid or fluid solution whichcan only exist at pressures greater than ambient, the chemicalprecursor(s) are optionally first dissolved in primary solvent that isstable at ambient pressure. This solution is placed in a pressurecapable container, and then the secondary (or main) liquid or fluid(into which the primary solution is miscible) is added. The main liquidor fluid has a lower supercritical temperature, and results in loweringof the maximum temperature needed for the desired degree ofnebulization. By forming a high concentration primary solution, much ofthe resultant lower concentration solution is composed of secondary andpossible additional solution compounds. Generally, the higher the ratioof a given compound in a given solution, the more the solutionproperties behave like that compound. These additional liquids andfluids are chosen to aid in the very fine atomization, vaporization orgasification of the chemical precursor(s) containing solution. Choosinga final solution mixture with low supercritical temperature additionallyminimizes the occurrence of chemical precursors reacting inside theatomization apparatus, as well as lowering or eliminating the need toheat the solution at the release area. In some instances the solutionmay be cooled prior to the release area so that solubility and fluidstability are maintained. One skilled in the art of supercritical fluidsolutions could determine various possible solution mixtures withoutundue experimentation. Optionally, a pressure vessel with a glasswindow, or with optical fibers and a monitor, allows visualdetermination of miscibility and solute-solvent compatibility.Conversely, if in-line filters become clogged or precipitant is foundremaining in the main container, an incompatibility under thoseconditions may have occurred.

Another advantage is that release of fluids near or above theirsupercritical point results in a rapid expansion forming a high speedgas-vapor stream. High velocity gas streams effectively reduce the gasdiffusion boundary layer in front of the deposition surface which, inturn, improves film quality and deposition efficiency. When the streamvelocities are above the flame velocity, a pilot light or other ignitionmeans must be used to form a steady state flame. In some instances twoor more pilots may be needed to ensure complete combustion.Alternatively, instead of flames, the precursor can be passed throughhot gasses, plasma, laser or other energetic zones. With the plasmatorch and other energetic zones, no pilot lights are needed, and highvelocities can be easily achieved by following operational conditionsknown by one of ordinary skill in the art.

The solute-containing fluid need not be the fuel for the combustion.Noncombustible fluids like water N₂O or CO₂, or difficult to combustfluids like ammonia, can be used to dissolve the precursors or can serveas the secondary solution compound. These are then expanded into a flameor plasma torch which provides the environment for the precursors toreact. The depositions can be performed above, below or at ambientpressure. Plasma torches work well at reduced pressures. Flames can bestable down to 10 torr, and operate well at high pressures. Cool flamesof even less than 500° C. can be formed at lower pressures. While bothcan operate in the open atmosphere, it can be advantageous to practicethe methods of the invention in a reaction chamber under a controlledatmosphere to keep airborne impurities from being entrained into theresulting coating. Many electrical and optical coating applicationsrequire that no such impurities be present in the coating. Theseapplications normally require thin films, but thicker films for thermalbarrier, corrosion and wear applications can also be deposited.

Further bulk material can be grown, including single crystals, byextending the deposition time even further. The faster epitaxialdeposition rates provided by higher deposition temperatures, due tohigher diffusion rates, can be necessary for the deposition of singlecrystal thick films or bulk material.

CCVD is a flame process which utilizes oxygen. While it may be possibleusing CCVD to deposit oxygen-reactive materials with CCVD by depositingin the reducing portions of the flame, a better technique for depositingoxygen reactive materials, such as nickel, is a related processdescribed in U.S. patent application Ser. No. 09/067,975, filed Apr. 20,1998, the teachings of which are incorporated herein by reference.

The invention described in referenced U.S. patent application Ser. No.09/067,975 provides an apparatus and method for chemical vapordeposition wherein the atmosphere in a coating deposition zone isestablished by carefully controlling and shielding the materials fed toform the coating and by causing the gases removed from the depositionzone to pass through a barrier zone wherein they flow away from saiddeposition zone at an average velocity greater than 50 feet per minute,and preferably greater than 100 feet per minute. The rapid gas flowthrough the barrier zone essentially precludes the migration of gasesfrom the ambient atmosphere to the deposition zone where they couldreact with the coating or the materials from which the coating isderived. Careful control of the materials used to form the coating canbe provided by feeding the coating precursors in a fixed proportion in aliquid media. The liquid media is atomized as it is fed to a reactionzone wherein the liquid media is vaporized and the coating precursorsreact to form reacted coating precursors. Alternatively, the coatingprecursor(s) can be fed as a gas, either as itself or as a mixture in acarrier gas. The reacted coating precursors are often composed ofpartially, fully and fractionally reacted components, which can flow asa plasma to the deposition zone. The reacted coating precursors contactand deposit the coating on the surface of the substrate in thedeposition zone. A curtain of flowing inert gases may be provided aroundthe reaction zone to shield the reactive coating materials/plasma inthat zone from contamination with the materials used in the surroundingapparatus or with components of the ambient atmosphere.

The vaporization of the liquid media and reaction of the coatingprecursors in the reaction zone requires an input of energy. Therequired energy can be provided from various sources, such as electricalresistance heating, induction heating, microwave heating, RF heating,hot surface heating and/or mixing with hot inert gas.

Herein, non-combustion process will be referred to as “ControlledAtmosphere Combustion Chemical Vapor Deposition” (CACCVD). Thistechnique provides a relatively controlled rate of energy input,enabling high rates of coating deposition. In some preferred cases, theliquid media and/or a secondary gas used to atomize the liquid media canbe a combustible fuel used in the CACCVD. Particularly important is thecapability of CACCVD to form high quality adherent deposits at or aboutatmospheric pressure, thereby avoiding the need to be conducted inelaborate vacuum or similar isolation housings. For these reasons, inmany cases, CACCVD thin film coatings can be applied in situ, or “in thefield”, where the substrate is located.

Combustion chemical vapor deposition (CCVD) is not suitable for thosecoating applications which require an oxygen free environment. For suchapplications, CACCVD, which employs non-combustion energy sources suchas hot gases, heated tubes, radiant energy, microwave and energizedphotons as with infrared or laser sources are suitable. In theseapplications it is important that all of the liquids and gases used beoxygen-free. The coating precursors can be fed in solution or suspensionin liquids such as ammonia or propane which are suitable for the depositof nitrides or carbides, respectively.

CACCVD processes and apparatus provide control over the deposition zoneatmosphere, thereby enabling the production of sensitive coatings ontemperature sensitive or vacuum sensitive substrates, which substratescan be larger than could otherwise be processed by conventional vacuumchamber deposition techniques.

A further advantage of CACCVD is its ability to coat substrates withoutneeding additional energy supplied to the substrate. Accordingly, thissystem allows substrates to be coated which previously could notwithstand the temperatures to which substrates were subjected by mostprevious systems. For instance, nickel coatings can be provided onpolyamide sheet substrates without causing deformation of the substrate.Previously atmospheric pressure deposition techniques were unable toprovide chemical vapor deposition of metallic nickel because of itsstrong affinity to oxygen, while vacuum processing of polyamide sheetsubstrates was problematical due to its outgassing of water and tendencytoward dimensional instability when subjected to heat and vacuum.

The present invention is directed particularly to the formation of thinlayer capacitors, it is preferred that at least one layer of suchcapacitors being conveniently deposited by CCVD or CACCVD. Generally, acapacitor comprises a pair of electrically conductive plates with adielectric material interposed between the plates, whereby the platesare capable of holding an electrical charge. Thin layer capacitorsformed in accordance with the invention involve the formation of a thinlayer of dielectric material in intimate contact with electricallyconducting plate layers.

As a simple configuration of a thin layer capacitor, a dielectricmaterial layer may be formed on a metal foil or metal layer, and asecond metal layer formed on the opposite surface of the dielectricmaterial layer. Such a three layer structure is itself a capacitor andmay be used, as such, as a decoupling capacitor.

Using the three-layer structure described in the above paragraph, aplurality of discrete capacitors can be formed by patterning at leastone of the electrically conductive layers, typically the second metallayer formed on the dielectric layer. Such patterning of the metal layercan be accomplished by conventional photoresist techniques followed byetching of the metal layer so as to form a pattern of discrete plates onone surface of the dielectric material layer. In such a structure, theother metal layer, e.g., the metal foil layer, serves as a commoncapacitor plate for holding charge relative to the opposed discretecapacitor plates. Alternatively, both metal layers may be patterned byphotoresist/etching techniques.

Instead of the first layer being a metal foil, the first layer may alsobe a thin metal layer deposited on a polymeric film, e.g., a polyamidefilm. Subsequently, a dielectric material layer and a second metal layerare deposited thereon. The second metal layer may be patterned asdescribed above to form discrete capacitor plates.

It is also possible to pattern a dielectric material layer byphotoresist/etching techniques. For example, silica based glasses,deposited as thin dielectric material layers in accordance with theinvention, may be etched with ammonium hydrogen difluoride, fluoroboricacid, and mixtures thereof.

Capacitor configurations are described, for example, in U.S. Pat. Nos.5,079,069, 5,155,655, and 5,410,107, the teachings of each of which areincorporated by reference.

Thin layer capacitors for printed circuit boards require large areas andsome flexibility for reasons having to do with handling, robustness,flow weight and thermal expansion of the materials, etc., and layeredstructures from which the capacitors are formed must have someflexibility. This is to be distinguished from the smaller more rigidstructures of silicon chip technology. Because flexibility is requiredand because the dielectric materials used herein are generally glassy,e.g., silica, the dielectric layers are necessarily very thin, i.e., 2microns or thinner, preferably 1 micron or thinner.

The substrate material should be thing capable of being rolled andshould be available in many widths, and long lengths. Materials such asmetals foils and polymers satisfy these needs while silicon does not.Silicon is easier to deposit on by most techniques because it is stiff,does not out-gas and is of small size. CCVD is able to coat the desiredsubstrates with quality coatings.

SUMMARY OF THE INVENTION

In accordance with the present invention thin layer capacitors areformed on a flexible substrate, which capacitors may be embedded withina printed circuit board. On a flexible substrate is formed a thin layerof dielectric material. Preferably, the dielectric material is depositedon the substrate by combustion chemical vapor deposition (CCVD).

In one embodiment of the invention, a dielectric layer is deposited on ametal foil, such as copper, nickel or aluminum foil. Then, on theopposite side of the dielectric layer is deposited a second conductinglayer, usually of metal. The second conductive layer may be depositedentirely by CCVD, or CACCVD. Alternatively, a seed layer, such as a thinlayer of platinum, may be deposited by CCVD and then a thicker metallayer built up by electroplating to form the three-layer capacitorstructure. Such a three-layer structure may, without further processing,act as a capacitor, e.g., a decoupling capacitor, or the three-layerstructure may be further processed to form a multi-capacitor component.The thin layer capacitor structures described herein, are typicallyembedded in dielectric material, e.g., epoxy-based prepreg, so as tofunction as a capacitor layer within an electronic circuit board.

Embedded capacitors of the type taught in accordance with the inventionenable further miniaturization of printed circuit boards (PCBs) becausefabrication no longer requires discrete capacitors that have to be largeenough to be handled either by robot arms and or humans and soldered tothe traces on the face of a printed circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of the apparatus of the invention.

FIG. 2 shows a schematic diagram of an apparatus for the deposition offilms and powders using near supercritical and supercriticalatomization.

FIG. 3 shows a detailed schematic view of the atomizer used in thepresent invention.

FIGS. 4A, 4B and 4C are cross-sectional views of capacitors comprisingor formed from a three-layer structure of a metal foil, a dielectriclayer, and a deposited metal layer.

FIGS. 5A and 5B are cross-sectional views of a four layer capacitorstructures of a polymeric film, a first deposited metal layer, adielectric material layer, and a second deposited metal layer.

FIG. 6 is a cross-sectional view of a 5-layer structure including ametal foil, a barrier layer, a dielectric layer, an adhesion layer and adeposited metal layer.

FIG. 7 is a schematic view, partially in section, of an apparatus forapplying coatings in accord with the present invention.

FIG. 8 is a close-up perspective view, partially in section, of aportion of the coating head used in the apparatus of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention may be understood more readily by reference to thefollowing detailed description of preferred embodiments of the inventionand the Figures.

It is to be understood that the terminology used herein is for thepurpose of describing particular embodiments only and is not intended tobe limiting. It must be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise.

Throughout this application, where publications are referenced, thedisclosures of these publications in their entireties are herebyincorporated by reference into this application in order to more fullydescribe the state of the art to which this invention pertains.

The present invention provides a method for coating a substrate with aselected material. The method comprises, at a first selected temperatureand a first selected pressure, dissolving into a suitable carrier tothereby form a transport solution one or more reagents capable ofreacting (where, for a single precursor reagent, the precipitation ofthe reagent from the solution or change in chemical bonds is hereinconsidered a “reaction”) to form the selected material. At some timeprior to the actual deposition, a substrate is positioned in a regionhaving a second selected pressure. The second selected pressure can beambient pressure and is generally above 20 torr. The transport solutionis then pressurized to a third selected pressure above the secondselected pressure using a pressure regulating means. One of skill in theart would recognize that there are many suitable pressure regulatingmeans, including, but not limited to compressors, etc. Next, thepressurized, transport solution is directed to a fluid conduit having aninput end and an opposed output end having a temperature regulatingmeans positioned thereon for regulating the temperature of the solutionat the output end. The output end of the conduit further comprises anoutlet port oriented to direct the fluid in the conduit into the regionand in the direction of the substrate. The outlet port can be of a shapesimilar to a nozzle or restrictor as used in other spraying andatomizing applications. Thereafter, the solution is heated using thetemperature regulating means to a second selected temperature within 50°C. above or below the critical temperature, T_(c), of the solution whilemaintaining the third selected pressure above the second selectedpressure and above the corresponding liquidus or critical pressure,P_(c) of the solution at the second selected temperature using thepressure regulating means. Then, the pressurized, heated solution isdirected through the outlet port of the conduit into the region toproduce a nebulized solution spray in the direction of the substrate. Asthe solution is directed into the region, one or more selected gases areadmixed into the nebulized solution spray to form a reactable spray and,thereafter, this reactable spray is exposed to an energy source at aselected energization point. The energy source provides sufficientenergy to react the reactable spray (which contains the one or morereagents of the transport solutions) thereby forming the material andcoating the substrate therewith.

In a further embodiment of this method, the energy source comprises aflame source and the selected energization point comprises an ignitionpoint. In an alternate embodiment, The energy source comprises a plasmatorch and heated gasses.

In a further embodiment of the method, the second selected pressure ofthe region is ambient pressure.

In yet another embodiment, the nebulized solution spray is a vapor or anaerosol having a maximum droplet size of less than 2 μm.

In a further embodiment, the second selected pressure of the region isreduced to produce a combustion flame having a temperature of less than1000° C.

In yet another embodiment, the carrier is propane and the transportsolution comprises at least 50% by volume propane. In a furtherembodiment, the transport solution further includes butanol, methanol,isopropanol, toluene, or a combination thereof. In yet anotherembodiment, the carrier is selected such that the transport solution issubstantially precipitate free at standard temperature and pressure fora period of time sufficient to carry out the method.

In an alternate embodiment of the method, a pressurized container isused and before, during or after the pressuring step, a standardtemperature and pressure gas is also contacted with the transportsolution at a selected pressure sufficient to form a liquid orsupercritical fluid (depending upon the temperature). In a preferredembodiment, the transport solution containing the standard temperatureand pressure gas is substantially precipitate free at the selectedpressure for a period of time sufficient to carry out the method. In yetanother embodiment, the reagent concentration of the transport solutionis between 0.0005 M and 0.05 M.

In a further embodiment, the outlet end of the conduit further comprisesa fluid introduction port and, prior to directing the pressurized,heated solution through the outlet port of the conduit, fluid is addedto the pressurized, heated solution through the fluid introduction port.Such introduction forms a combined solution having a reducedsupercritical temperature.

In yet another embodiment, each of the one or more reagents has a vaporpressure of no less than about 25% of the vapor pressure of the carrier.

In a further embodiment, the outlet end of the conduit comprises tubinghaving an internal diameter of 2 to 1000 μm, more preferably 10 to 250μm. In a more preferable embodiment, the outlet end of the conduitcomprises tubing having an internal diameter of 25 to 125 μm. In yet afurther preferable embodiment, the outlet end of the conduit comprisestubing having an internal diameter of 50 to 100 μm.

In another embodiment, the temperature regulating means comprises meansfor resistively heating the conduit by applying thereto an electriccurrent of a selected voltage from an electric current source. In apreferred embodiment, the voltage is less than 115 Volts. In yet anotherpreferred embodiment, the means for resistively heating the conduitcomprises a contact positioned within 4 mm of the outlet port.

Moreover, the present invention also provides the above method whereinthe carrier and one or more reagents are selected such that the secondselected temperature is ambient temperature.

The above method may be practiced wherein the material that coats thesubstrate comprises a metal, a metal or metalloid oxide, or a mixture ofa metal with a metal or metalloid oxide.

In a further embodiment, the reactable spray comprises a combustiblespray having a combustible spray velocity and wherein the combustiblespray velocity is greater than the flame speed of the flame source atthe ignition point and further comprising one or more ignitionassistance means for igniting the combustible spray. In a preferredembodiment, each of the one or more ignition assistance means comprisesa pilot light. In yet another embodiment, the combustible spray velocityis greater than mach one.

In a further embodiment, the ignition point or flame front is maintainedwithin 2 cm. of the outlet port.

The present invention also provides a method where, during the exposingstep, cooling the substrate using a substrate cooling means. In apreferred embodiment, the substrate cooling means comprises a means fordirecting water onto the substrate. However, one of ordinary skill inthe art would recognize that many other suitable cooling means could beused.

In a further embodiment, the material that coats the substrate has athickness of less than 500 nm. In yet another embodiment, the materialthat coats the substrate comprises a graded composition. In anotherembodiment, the material that coats the substrate comprises an amorphousmaterial. In a further embodiment, the material that coats the substratecomprises a nitride, carbide, boride, metal or other non-oxygencontaining material.

The present invention also provides a method further comprising flowinga selected sheath gas around the reactable spray thereby decreasingentrained impurities and maintaining a favorable deposition environment.

In a preferred embodiment, the second selected pressure is above 20torr.

Referring now to FIG. 1, the preferred apparatus 100 comprises apressure regulating means 110, such as a pump, for pressurizing to afirst selected pressure a transport solution T (also called “precursorsolution”) in a transport solution reservoir 112, wherein the transportsolution T comprises a suitable carrier having dissolved therein one ormore reagents capable of reacting to form the selected material andwherein the means for pressurizing 110 is capable of maintaining thefirst selected pressure above the corresponding liquids (if thetemperature is below T_(c)) or critical pressure, P_(c), of thetransport solution T at the temperature of the transport solution T, afluid conduit 120 having an input end 122 in fluid connection with thetransport solution reservoir 112 and an opposed output end 124 having anoutlet port 126 oriented to direct the fluid in the conduit 120 into aregion 130 of a second selected pressure below the first selectedpressure and in the direction of the substrate 140, wherein the outletport 126 further comprises means 128 (see FIGS. 2 and 3, atomizer 4) fornebulizing a solution to form a nebulized solution spray N, atemperature regulating means 150 positioned in thermal connection withthe output end 124 of the fluid conduit 120 for regulating thetemperature of the solution at the output end 124 within 50° C. above orbelow the supercritical temperature, T_(c), of the solution, a gassupply means 160 for admixing one or more gases (e.g., oxygen) (notshown) into the nebulized solution spray N to form a reactable spray, anenergy source 170 at a selected energization point 172 for reacting thereactable spray whereby the energy source 170 provides sufficient energyto react the reactable spray in the region 130 of the second selectedpressure thereby coating the substrate 140.

In a further embodiment of the apparatus, the energy source 170comprises a flame source and the selected energization point 172comprises an ignition point. In an alternate embodiment, the energysource 170 comprises a plasma torch. In yet another embodiment, theoutlet port 126 further comprises a pressure restriction (see FIG. 3,restrictor 7).

In a further embodiment of the apparatus, the second selected pressureof the region is ambient pressure.

In yet another embodiment, the nebulized solution spray N is a vapor oran aerosol having a maximum droplet size of less than 2 μm.

In a further embodiment, the second selected pressure of the region isreduced to produce a combustion flame having a temperature of less than1000° C.

In yet another embodiment, the carrier is propane and the transportsolution comprises at least 50% by volume propane. In a furtherembodiment, the transport solution further includes butanol, methanol,isopropanol, toluene, or a combination thereof. In yet anotherembodiment, the carrier is selected such that the transport solution issubstantially precipitate free at standard temperature and pressure fora period of time sufficient to carry out the method.

In an alternate embodiment of the apparatus, a pressurized container(not shown) is provided and a standard temperature and pressure gas isalso contacted with the transport solution at a selected pressuresufficient to form a liquid or supercritical fluid. In a preferredembodiment, the transport solution containing the standard temperatureand pressure gas is substantially precipitate free at the selectedpressure for a period of time sufficient to carry out the method. In yetanother embodiment, the reagent concentration of the transport solutionis between 0.0005 M and 0.05 M.

In a further embodiment, the outlet end 124 of the conduit 120 furthercomprises a fluid introduction port (see FIG. 2, feed lines 17 or 19)and, prior to directing the pressurized, heated solution through theoutlet port 126 of the conduit 120, fluid is added to the pressurized,heated solution through the fluid introduction port. Such introductionforms a combined solution having a reduced supercritical temperature.

In yet another embodiment, each of the one or more reagents has a vaporpressure of no less than about 25% of the vapor pressure of the carrier.

In a further embodiment, the outlet end of the conduit comprises tubinghaving an internal diameter of 2 to 1000 μm, more preferably 10 to 250μm. In a more preferable embodiment, the outlet end of the conduitcomprises tubing having an internal diameter of 25 to 125 μm. In yet afurther preferable embodiment, the outlet end of the conduit comprisestubing having an internal diameter of 50 to 100 μm.

In another embodiment, the temperature regulating means 150 comprisesmeans for resistively heating the conduit by applying thereto anelectric current of a selected voltage from an electric current source.In a preferred embodiment, the voltage is less than 115 Volts. In yetanother preferred embodiment, the means for resistively heating theconduit comprises a contact 152 positioned within 4 mm of the outletport 126.

Moreover, it is provided that the above apparatus is utilized whereinthe carrier and one or more reagents are selected such that the secondselected temperature is ambient temperature.

The above apparatus may be used wherein the material that coats thesubstrate 140 comprises a metal. Alternatively, the material that coatsthe substrate 140 comprises one or more metal oxides. In yet a furtherembodiment, the material that coats the substrate 140 comprises at least90% silica.

In a further embodiment, the reactable spray comprises a combustiblespray having a combustible spray velocity and wherein the combustiblespray velocity is greater than the flame speed of the flame source atthe ignition point 172 and further comprising one or more ignitionassistance means 180 for igniting the combustible spray. In a preferredembodiment, each of the one or more ignition assistance means 180comprises a pilot light. In yet another embodiment, the combustiblespray velocity is greater than mach one.

In a further embodiment, the ignition point 172 or flame front ismaintained within 2 cm. of the outlet port.

The present invention also provides a substrate cooling means 190 forcooling the substrate 140. In a preferred embodiment, the substratecooling means 190 comprises a means for directing water onto thesubstrate 140. However, one of ordinary skill in the art would recognizethat many other suitable cooling means could be used.

In a further embodiment, the material that coats the substrate 140 has athickness of less than 500 nm. In yet another embodiment, the materialthat coats the substrate 140 comprises a graded composition.

There is further an apparatus provided comprising a means (see FIGS. 2and 3, feed line 17 or 19) for flowing a selected sheath gas around thereactable spray thereby decreasing entrained impurities and maintaininga favorable deposition environment.

In a preferred embodiment, the second selected pressure is above 20torr.

In a further embodiment of the method, the energy source comprises aflame source and the selected energization point comprises an ignitionpoint. In an alternate embodiment, the energy source comprises a plasmatorch, hot gasses, etc.

In a further preferred embodiment of the powder forming method, thetransport solution concentration is between 0.005 M and 5 M.

To simplify the operation, it is helpful to pump the precursor/solventsolution to the atomizing device at room temperature. Heating of thesolution should occur as a final step just prior to release of thesolution into the lower pressure region. Such late stage heatingminimizes reactions and immiscibilities which occur at highertemperatures. Keeping the solution below the supercritical temperatureuntil atomization maintains the dissolved amounts of precursor in theregion of normal solubility and reduces the potential of developingsignificant solvent-precursor concentration gradients in the solution.These solubility gradients are a result of the sensitivity of thesolution strength of a supercritical solvent with pressure. Smallpressure gradients (as they can develop along the precursor-solventsystem delivery) can lead to significant changes in solubility as hasbeen observed. For instance, the solubility of acridine in carbondioxide at 308° K can be increased 1000 times by increasing the pressurefrom 75 atm to 85 atm. See V. Krukonis, “Supercritical Fluid Nucleationof Difficult to Comminute Solids”, Presented at AIChE Meeting, SanFrancisco, Nov. 25-30, 1984. Such solubility changes are potentiallydetrimental because they may cause the precursor to be driven out ofsolution and precipitate or react prematurely, clogging lines andfilters.

The rapid drop in pressure and the high velocity at the nozzle cause thesolution to expand and atomize. For solute concentrations in the normalsolubility range, preferred for operation of the near supercriticalatomization system of the present invention, the precursors areeffectively still in solution after being injected into the low pressureregion. The term “effectively in solution” must be understood inconjunction with processes taking place when a solution with soluteconcentrations above the normal solvent strength is injected into thelow pressure region. In this case, the sudden pressure drop causes highsupersaturation ratios responsible for catastrophic solute nucleationconditions. If the catastrophic nucleation rapidly depletes the solventfrom all dissolved precursor, the proliferation of small precursorparticles is enhanced. See D. W. Matson, J. L. Fulton, R. C. Petersenand R. D. Smith, “Rapid Expansion of Supercritical Fluid Solutions:Solute Formation of Powders, Thin Films, and Fibers”, Ind. Eng. Chem.Res., 26, 2298 (1987); H. Anderson, T. T. Kodas and D. M. Smith, “VaporPhase Processing of Powders: Plasma Synthesis and AerosolDecomposition”, Am. Ceram. Soc. Bull., 68, 996 (1989); C. J Chang and A.D Randolph, “Precipitation of Microsize Organic Particles fromSupercritical Fluids”, AIChE Journal, 35, 1876 (1989); T. T. Kodas,“Generation of Complex Metal Oxides by aerosol Processes:Superconducting Ceramic Particles and Films”, Adv. Mater., 6, 180(1989); E. Matijevic, “Fine Particles: Science ad Technology”, MRSBulletin, 14, 18 (1989); E. Matijevic, “Fine Particles Part II:Formation Mechanisms and Applications”, MRS Bulletin, 15, 16 (1990); R.S. Mohamed, D. S. Haverson, P. G. Debenedetti and R. K. Prud'homme,“Solid Formation After Expansion of Supercritical Mixtures,” inSupercritical Fluid Science and Technology, edited by K. P. Johnston andJ. M. L. Penniger, p.355, American Chemical Society, Washington, D.C.(1989); R. S. Mohamed, P. G. Debenedetti and R. K. Prud'homme, “Effectsof Process Conditions on Crystals Obtained from Supercritical Mixtures”,AIChE J., 35, 325 (1989); J. W. Tom and P. G. Debenedetti, “Formation ofBioerodible Polymeric Microspheres and Microparticles by Rapid Expansionof Supercritical Solutions”, Biotechnol. Prog., 7, 403 (1991). Particlesare undesirable for the formation of thin coatings, but can bebeneficial during the formation of powders.

Thus the heated atomizer provides the further superior advantages,compared to an unheated device that operates on rapid expansion of asolvent at exclusively above the supercritical temperature, that (1) thetemperature allows for a well controlled degree of atomization of theprecursor-solvent mixture and (2) catastrophic nucleation of theprecursors can be omitted while still enjoying the benefits ofsupercritical atomization. Supersonic velocities can be created forminga mach disk which additionally benefits atomization. Addition of gassesto the released atomized materials aids in directing the flow and canensure a desired mixture for combustion.

By adjusting the heat input into the atomizing device, the liquidsolution can be vaporized to various degrees. With no heat input to theatomizing device, liquid solutions of higher supercritical temperatureliquids, that are liquids at STP, can exit in the form of a liquidstream which is clearly far from a supercritical condition. This resultsin a poorly formed flame and, possibly, undesirable liquid contact withthe substrate. Decreasing the temperature differential of the liquidsolution to its supercritical temperature at the nozzle causes theliquid solution to break up into droplets forming a mist which isreleased from the atomizing device. The droplets vaporize, and thusbecome invisible, after a short distance. As the supercriticaltemperature at the atomizing device is approached, the liquid solutiondroplets decrease in size, and the distance to solution vaporization isdecreased. Using this atomizer the vapor droplet size was determinedusing an laser aerosol particle size tester and the obtained dropletsize was below the 1.8 Nm detection limit of the instrument.

Further increasing the heat input results in a state of no mist at thetip, or complete vaporization. Without wishing to be bound by theory,this behavior of the solution can be attributed to the combinedsupercritical properties of the reagents and solvents. Solutions ofprecursors in lower supercritical temperature solvents, that are gassesat STP, behave similarly, but the emerging solution from the tip (alsoreferred to as the “nozzle” or “restrictor”) does not form a liquidstream, even without heat input. The amount of heat needed to obtainoptimal vaporization of the solution depends mostly on the heat capacityof the solution and the differential between the supercriticaltemperature of the solvent and the ambient temperature around thenozzle.

It is desirable to maintain the pressure and temperature of the system(before vaporization) above the boiling and the supercritical point ofthe solution. If the pressure falls below the liquidus or criticalpressure, coincident with the temperature above the boiling point,vaporization of the solvents will occur in the tube prior to the tip.This leaves the solutes which can build up and clog the atomizingdevice. Similarly the pressure is preferably sufficiently high in thesupercritical region so that the fluid is more liquid-like. Liquid-likesupercritical fluids are better solvents than more gas-likesupercritical fluids, further reducing the probability of solutesclogging the atomizing device. If the precursor-to-precursor interactionis higher than the strength between solvent and precursor, thesolvent-precursor bonds can be broken and effectively drive theprecursor out of solution. Precursor molecules then form clusters thatadhere to the atomizing device and clog the restrictor. The problem canbe solved, in most cases, by shifting the vaporization point from theinside of the tip to the end of the tip, which is accomplished byreducing the heat input into the atomizing device. Another solution isto use a solvent which forms stronger bonds with the precursor so a morestable solution is formed. A small amount of mist at the tip usuallyresults in the best quality thin films. Nano- or micro-spheres of thematerial will form if the temperature of the solution it too high or toolow. These spheres are detrimental if dense coatings are desired.

If the no-mist condition is reached, the deposition is being performedabove the critical temperature. The heat of the flame and mixing withexternal gasses keeps STP liquid solvents from condensing and formingdroplets. In the no-mist instance, atomization and intermixing is verygood but flow stability is reduced, resulting in a flame that can jumpfrom side to side with respect to the direction of the tip. With such aflame behavior, depositions remain possible, but it can be difficult todeposit films requiring stringent thickness uniformity. Additionally, itis necessary to maintain the temperature of the solution, prior torelease, below the temperature where either the solute precipitates orreacts and precipitates. When using a solvent mixture it may be possibleduring heating to cross the line for spinoidal immiscibility. Thiscauses the formation of two separate phases, with the possibility ofconcentration differences in the two phases due to differentsolubilities of the solutes. This may influence the formation ofprecursor and product spheres at high atomization temperatures. All ofthese factors demonstrate the preferability of minimizing the solution'sexposure to heating, if necessary, until the tip so that possibleunwanted equilibrium condition states of matter do not have sufficienttime to transpire. The structure of the films deposited can thus beprecisely controlled.

Due to this control, a number of film microstructures are possible. Byincreasing solution concentration it is possible to increase thedeposition rate and the following microstructural changes result withincreasing solution concentration; dense to porous, specular to dull,smooth to rough, columnar to hillocks, and thin to thick. Graded andmultilayered coatings can also be produced. Multilayers can be formed bysupplying different precursor containing solutions to an individualflame. Sequential multiple deposition flames may be used to increasethroughput for production applications. Some additional factorscontrolling deposition parameters include; substrate surface temperaturewhich controls surface diffusion and nucleation; pressure which controlsboundary layer thickness and thus deposition rate, solution compositionand mix gasses varies the material being deposited and thus the coatingsgrowth habit, flame and plasma energy level effects where the reactionoccurs and vapor stability, and the distance to the substrate effectsthe time from nebulization to reaction to deposition which can lead toparticle formation or increased diffusion time for larger clusters.Additionally, electric and magnetic fields affect the growth habits ofsome materials, or increase deposition efficiency. One of ordinary skillin the art would recognize that such electric and magnetic fields willaffect the growth habits of some vapor deposited materials, as well asvary the particular deposition rate and efficiency.

Because the required energy input into the solution heating atomizervaries for different precursor/primary-solvent/secondary-solventsolutions, it is preferred to deposit multilayer thin films fromsolutions with constant primary to secondary solvent ratios. In sodoing, it is not necessary to change the energy input to the atomizerwhen switching from one solution to another solution. The resultingsimplification of the setup produces increased performance andreliability while reducing costs. Alternatively, the substrate can bepassed by flames containing different reagents to build the desiredmultilayer.

When the solution provides the fuel for combustion, concentrations up to0.1 molar result in dense coatings depending on the material. Mostmaterials have preferred concentrations of up to 0.01 molar. Materialswith lower diffusion and mobility need solution concentrations of lessthan 0.002. Solution concentrations of less than 0.0001 molar result invery slow deposition rates for most materials. Flame depositions withadded combustible materials can have higher concentrations, evenexceeding 1 M, but for the preferable vapor formation of the precursors,high concentrations are less desirable unless the precursor(s) have highvapor pressures. Low vapor pressure precursor solution concentrationsare preferably less than 0.002 molar.

Without wishing to be bound by theory, it is helpful to understand thatthe principle of the deposition technique of the present inventioninvolves the finding that CVD its not limited to reactions at thesurface. See Hunt, A. T., “Combustion Chemical Vapor Deposition, a NovelThin Film Deposition Technique”, Ph.D. Thesis Georgia Inst. of Tech,Atlanta, Ga., (1993); Hunt, A. T., “Presubstrate Reaction CVD, and aDefinition for Vapor”, presented at the 13th Int. Conf. on CVD, LosAngles, Calif. (1996), the contents of which are hereby incorporated bythis reference. Reactions can occur predominately in the gas stream, butthe resulting material which is deposited must be subcritical in size toyield a coating with vapor deposited microstructures. These observationsdemonstrate that a vapor is composed of individual atoms, molecules ornanoclusters which can be absorbed onto a substrate and readily diffusedinto lower energy sites or configurations. Thus the maximum cluster sizemust decrease with lower substrate temperatures as does the criticalnucleus size. It is known by one of ordinary skill in the art thatreagent clusters are left after vaporization of the solvents, and thecluster size is related to the reagent vapor pressure, initial dropletsize and the solution concentration. Therefore, atomization of low vaporpressure reagents, which therefore do not gasify in the flame, must bevery fine to form vapor.

Preferred liquid solvents are low cost solvents include, but are notlimited to, ethanol, methanol, water, isopropanol and toluene. Watersolutions must be fed into a preexisting flame, while the combustiblesolvents can themselves be used to form the flame. It is preferable, butnot required, to form the bulk of the flame using the solution ratherthan feeding the solution into a flame. Lower reagent concentrationresults this way, which eases the formation of subcritical nucleus sizedmaterials.

One preferred solvent and secondary solution fluid which is propane,which is a gas at STP. However, it must be noted that many other solventsystems are operable. See, e.g., CRC Handbook of Chemistry and Physics,CRC Press, Boca Raton, Fla. Propane is preferred because of its lowcost, its commercial availability, and its safety. Many low costorganometalics can be used in a predominately propane solution. To easehandling, the initial precursors can be dissolved in methanol,isopropanol, toluene or other solvents compatible with propane. Thisinitial solution is then placed into a container into which liquidpropane is added. Propane is a liquid at above only about 100 psi atroom temperatures. The resulting solution has a much lower supercriticalpoint than the initial solution which eases atomization by lowering therequired energy input into the atomizer. Additionally, the primarysolvent acts to increase the polar solubility of the propane, thusallowing higher solution concentrations for many reagents than wouldotherwise be achieved by propane alone. As a general rule, the polarityof the primary solvent should increase with increasing polarity of thesolute (precursor). Isopropanol can thus aid in the solubility of apolar solute better than toluene. In some cases the primary solvent actsas a shield between the secondary solvent and a ligand on the solute.One example is the dissolution of platinum-acetylacetonate[Pt(CH₃COCHCOCH₃)₂] in propane, where the weight ratios betweenprecursor/primary solvent and primary solvent/secondary solvent can behigher than those required in other systems.

Ammonia has been considered and tested as a secondary solvent for thedeposition of coatings and powders. While ammonia is an inexpensivesolvent that is compatible with some nitrate based precursors, it is noteasily usable with other secondary solvents and problems stem from thegeneral aggressiveness of pure ammonia. The atomization properties ofammonia were tested without the addition of a precursor and the usedpressure vessel was significantly attacked after the experiment evenwhen an inert Type-316 stainless steel vessel was used. In contrast tohydrocarbon based solvents, ammonia also renders Buna-N and Vitongaskets useless after only a few minutes. Even with a suitable gasketmaterial this is a problem since the desired coatings or powders usuallymust not contain traces of iron or other elements leached from thepressure vessel wall. However, there are materials, such as EPDMelastomer which may be used. Ni has been deposited from a ammonia-watermix with Ni-amine-nitrate formed precursor.

Other gas-like secondary solvents that were tested and can be usedinclude ethane, ethylene, ethane/ethylene mixture, propane/ethylenemixture, and propane/ethane mixture. Platinum thin films were depositedfrom a supercritical mixture of ethane and a platinum metalorganic.

Other tested solvents and solvent mixtures resulted in similar quality,but were more complex to work with since their boiling points aresignificantly lower, which required cooling of the solution or very highpressures. The ease of handling makes propane the preferred solvent butthe other supercritical solvents are considered alternatives to propanein cases where propane cannot be used, such as when a precursor that issoluble in propane cannot be found. Other fluids can be used to furtherreduce the supercritical temperature if desired.

One heating method is the application of an electric current between thenozzle end, where the precursor solution is injected into the lowpressure region, and the back of the restriction tube. This directlyheated restrictive tube method allows for fast changes in atomizationdue to a short response time. The location of most intense heating canbe shifted toward the tip by increasing the connection resistancebetween the tip and the electrical lead connected to the tip. Thinwalled restriction tubes possess a larger resistance than thick walledtubes and decrease the response time. Other heating methods can beapplied and several have been investigated, including but not limitedto, remote resistive heating, pilot flame heating, inductive heating andlaser heating. One of ordinary skill in the art could readily determineother suitable heating means for regulating the temperature at theoutlet port of the atomizer.

Remote resistive heating uses a non-conducting restriction tube that islocated inside an electrically heated tube. The non-conducting tube willfit tightly into the conductive tube. Application of an electric currentto the conductive type heats that tube and energy is transferred intothe inner, non-conductive restriction tube. This method requires largerheating currents compared to the directly-heated restrictive tube methodand shows longer response times, which can be advantageous under certainconditions since the increased response time results in a high degree ofthermal stability. On the other hand, pilot flame and laser heating usethe energy of the pilot flame or laser light, respectively, to heat therestriction tube. This can be done in a directly heated setup where thetip of the restriction tube is subjected to the pilot flame or laserlight or in an indirectly heated configuration where the larger outertube is heated. Because the amount of energy that needs to betransferred into the solution is quite large, the heated tube will,preferably, have a thicker wall than in the case of direct electricalheating or remote electrical heating. Subjecting an outer tube to thepilot flame or laser light allows the use of a thin walled restrictiontube.

Referring now to FIGS. 2 and 3, an apparatus 200 for the deposition offilms and powders using supercritical atomization is shown. Theapparatus 200 consists of a fixed or variable speed pump 1 that pumpsthe reagent transport solution 2 (also called “precursor solution”) fromthe solution container 3 into the atomizer (also referred to as the“nebulizer” or “vaporizer”) 4. FIG. 3 is an inset view showing a moredetailed schematic view of the atomizer 4. The precursor solution 2 ispumped from the precursor solution container 3 through lines 5 andfilters 6 and into the atomizer 4. The precursor solution 2 is thenpumped into a constant or variable temperature controlled restrictor 7.Heating can be accomplished in many ways including, but not limited to,resistive electrical heating, laser heating, inductive heating, or flameheating. For resistive electrical heating, either AC or DC current canbe used. One of the electrical connections 8 to the restrictor 7 ispreferably placed very close to the tip of the restrictor 7. In the caseof heating by a DC source, this connection 8 or pole can be eitherpositive or negative. The other pole 9 can be connected at any otherpoint along the restrictor 7, inside or outside the housing 10. Forspecial applications such as coating the inside of tubes, where a smalltotal atomizer size is advantageous, it is preferable to either connectto the restrictor 7 at the back of the housing 10 or to connect insidethe housing 10. Gas connections at the back of the housing 10 are shownin an on-line arrangement but can be placed in any other arrangementthat does not interfere with the function of the apparatus 200.

The thin gas A supply line 11, {fraction (1/16)}″ ID in most cases,carries a combustible gas mix to a small outlet 12 where it can serve asa stable pilot flame, preferably within 2.5 cm of the restrictor 7, forthe combustion of the precursor solutions supplied via the restrictor 7.Gas A supply is monitored by a flow controller 13, controlling the flowof the individual gas A mix components, 14 and 15. The gas A fuelcomponent 14 is mixed with the oxidizing component 15 in a mixing “T” 16close to or inside the atomizer 4. This late mixing is preferably forsafety reasons because it reduces potential flash-back. Distributionchannels inside the housing 10 connect the gas supply lines 11 to thegas A feed 17. Gas B supply lines 18 are used to deliver gas B from thesupply 19 such that good mixing with the nebulized solutions spray canbe accomplished. In most cases a high velocity gas stream is utilized. Anumber of gas B supply holes 20 (six for most cases, more or less holescan be used depending on the particular application) is placed aroundthe restrictor 7 supplying gas B such that the desired flow pattern isobtained. The flow properties of the gas B stream are influenced by suchfactors as gas B pressure in the gas B storage container 21, flow rateas determined by the flow controller 13, line diameters 5, and number ofsupply holes 20. Alternatively, gas B can be fed through a larger tubecoaxial to and surrounding the restrictor 7. Once the precursor solution2 has been pumped into the precursor supply 22 its temperature iscontrolled by the current flow (in the case. of electrical heating)through the restrictor 7 as determined by the power supply 23. Thisheating current can then be adjusted such that the proper amount ofatomization (nebulization, vaporization) can occur. The stable pilotflame is then capable of igniting the nebulized reactive spray anddepositing a powder or film on a substrate 24.

Many different coatings have been deposited using the methods andapparatuses described herein. While propane was used in most cases asthe super critical secondary solvent (i.e. a small amount of highprecursor concentration primary solvent was mixed with a large amount ofsecondary solvent), others solvents have been used. Other possiblesecondary solvents include, but are not limited to N₂O, ethylene,ethane, and ammonia.

One of ordinary skill in the art would recognize that almost anysubstrate can be coated by the method and apparatus of the presentinvention. A substrate can be coated if it can withstand the temperatureand conditions of the resulting hot gases produced during the process.Substrates can be cooled using a means for cooling (described elsewhereherein), such as a water jet, but at low substrate surface temperatures,dense or crystalline coatings of many materials are not possible becauseof the associated low diffusion rates. In addition, substrate stabilityin the hot gases can be further accounted for by using a lowtemperature, low pressure flame, either with or without additionalsubstrate cooling.

A variety of chemical precursors have been suggested for CCVD depositionof films and powders, and additional chemical precursors are suggestedherein. In addition to providing the metal or metalloid element, it isrequired of any chemical precursor for CCVD that it be soluble in asuitable carrier solvent, most desirably soluble in propane.Furthermore, if the precursor solution is to contain precursors of morethan one metal and/or metalloid, the chemical precursors must bemutually soluble in a suitable carrier solvent and chemically compatiblewith each other. If a precursor is not highly soluble in a primarysolvent, such as propane, it may be initially dissolved in a secondarysolvent, such as toluene, and subsequently introduced into the primarysolvent as a solution in the secondary solvent, providing that thechemical precursor does not precipitate when such a solution isintroduced into the primary solvent. Furthermore, cost considerationsenter into the choice of chemical precursor.

If a mixture of chemical precursors are to be provided for depositing alayer or powder of a particular composition, it is desirable that suchprecursors be combinable as a homogeneous “pre-solution” without theaddition of any additional solvent. If not, it is desirable that allchemical precursors be mutually soluble in a common solvent, the lesssolvent the better, as a “pre-solution”. These desired properties, ofcourse, facilitate shipping and handling, particularly when the intendedprimary solvent is propane or another material which is gaseous at roomtemperature. Though desirable to be able to provide a “pre-solution”, itis considered acceptable that the chemical precursors be mutuallysoluble in a deposition solution of one or more solvents and either beprepared and sold as such a solution or prepared on-site as a depositionsolution.

For deposition, the total concentration of the precursor compounds inthe carrier solvent is generally between about 0.001 and about 2.5 wt %,preferably between about 0.05 and about 1.0 wt %.

For most CCVD depositions, it is preferred that the precursors bedissolved in an organic solvent. However, for the capacitor materials towhich the present invention is directed, it is. undesirable that carbonco-deposits with the dielectric material. Next to the dielectric is the2nd electrode. Some conductive materials, nickel, for example, have ahigh affinity for carbon. Accordingly, precursors for such materials maybe preferably dissolved in an aqueous and/or ammonia solution, in whichcase, the aqueous and/or ammonia and/or N₂O solution would be aspiratedinto a hydrogen/oxygen flame for CCVD.

One of the advantages of CCVD, as performed with preferred atomizingapparatus, relative to other deposition methods, is that the a precursorsolution containing one or more dissolved chemical precursors isatomized as a near-super critical liquid or, in some cases, as a supercritical fluid. Accordingly, the amount of precursor or precursors beingburned and deposited on a substrate or deposited in powder form isindependent of the relative vapor pressures of the individual chemicalprecursors and the carrier solvent or solvents. This is in contrast toconventional CVD processes where individual supply lines must beprovided for each chemical precursor that is to be vaporized, generallywithin a carrier gas, for supply to a CVD furnace. Also, someconventional CVD precursors disproportionate, making it difficult tosupply such a chemical precursor uniformly—another problem readilyaddressed by CCVD technology.

A Controlled Atmosphere Combustion Chemical Vapor Deposition (CACCVD)apparatus is illustrated in FIGS. 7 and 8. A coating precursor 710 ismixed with a liquid media 712 in a forming zone 714, comprising a mixingor holding tank 716. The precursor 710 and liquid media 712 are formedinto a flowing stream which is pressurized by pump 718, filtered byfilter 720 and fed through conduit 722 to an atomization zone 724, fromwhich it flows successively through reaction zone 726, deposition zone728 and barrier zone 730. It is not required that a true solution beformed from mixing the coating precursor 710 with the liquid media 712,provided the coating precursor is sufficiently finely divided in theliquid media. However, the formation of a solution is preferred, since,generally, such produces a more homogeneous coating.

The flowing stream is atomized as it passes into the atomization zone724. Atomization can be accomplished by recognized techniques foratomizing a flowing liquid stream. In the illustrated apparatus,atomization is effected by discharging a high velocity atomizing gasstream surrounding and directly adjacent the flowing stream as itdischarges from conduit 722. The atomizing gas stream is provided from agas cylinder or other source of high pressure gas. In the illustratedembodiment, high pressure hydrogen (H₂) is used both as an atomizing gasand as a fuel. The atomizing gas is fed from hydrogen gas cylinder 732,through regulating valve 734, flowmeter 736 and into conduit 738.Conduit 738 extends concentrically with conduit 722 to the atomizationzone where both conduits end allowing the high-velocity hydrogenatomizing gas to contact the flowing liquid stream thereby causing it toatomize into a stream of fine particles suspended in the surroundinggas/vapors. This stream flows into the reaction zone 726 wherein theliquid media vaporizes and the coating precursor reacts to form areacted coating precursor, which often involves dissociation of thecoating precursor into ions of its components and results in a flowingstream of ionic particles, or plasma. The flowing stream/plasma, passesto the deposition zone 728 wherein the reacted coating precursorcontacts the substrate 740 depositing the coating thereon.

The flowing stream may be atomized by injecting the atomizing gas streamdirectly at the stream of liquid media/coating precursor as it exitsconduit 722. Alternatively, atomization can be accomplished by directingultrasonic or similar energy at the liquid stream as it exits conduit722.

The vaporization of the liquid media and reaction of the coatingprecursor require substantial energy input to the flowing stream beforeit leaves the reaction zone. This energy input can occur as it passesthrough the conduit 722, or in the atomization and/or reaction zones.The energy input can be accomplished by a variety of known heatingtechniques, such as electrical resistance heating, microwave or RFheating, electrical induction heating, radiant heating, mixing theflowing stream with a remotely heated liquid or gas, photopic heatingsuch as with a laser, etc. In the illustrated preferred embodiment, theenergy input is accomplished by the combustion of a fuel and an oxidizerin direct contact with the flowing stream as it passes through thereaction zone. This relatively new technique, referred to as CombustionChemical Vapor Deposition (CCVD), is more fully described in theincorporated U.S. Pat. No. 5,652,021. In the illustrated embodiment, thefuel, hydrogen, is fed from hydrogen gas cylinder 732, through aregulating valve, flowmeter 742 and into conduit 744. The oxidizer,oxygen, is fed from oxygen gas cylinder 746, through regulating valve748 and flowmeter 750 to conduit 752. Conduit 752 extends about andconcentric with conduit 744, which extends with and concentrically aboutconduits 722 and 738. Upon exiting their respective conduits, thehydrogen and oxygen combust creating combustion products which mix withthe atomized liquid media and coating precursor in the reaction zone726, thereby heating and causing vaporization of the liquid media andreaction of the coating precursor.

A curtain of a flowing inert gas provided around at least the initialportion of the reaction zone isolates the reactive gases from thematerials present in the apparatus located in proximity to the reactionzone. An inert gas, such as argon, is fed from inert gas cylinder 754,through regulating valve 756 and flowmeter 758 to conduit 760. Conduit760 extends about and concentric with conduit 752. Conduit 760 extendsbeyond the end of the other conduits 722, 738, 744 and 752, extendingclose to the substrate whereby it functions with the substrate 740 todefine a deposition zone 728 where coating 762 is deposited on thesubstrate generally in the shape of the cross-section of conduit 760. Asthe inert gas flows past the end of oxygen conduit 752, it initiallyforms a flowing curtain which extends about the reaction zone, shieldingthe reactive components therein from conduit 760. As it progresses downthe conduit 760, the inert gas mixes with the gases/plasma from thereaction zone and becomes part of the flowing stream directed to thedeposition zone 728.

An ignition source is needed to initially ignite the hydrogen andoxygen. A separate manually manipulated lighting or ignition device issufficient for many applications, however the use of such may require atemporary reduction in the flow of inert gas until a stable flame frontis established. In some applications, the total flow of gas may be toogreat to establish an unassisted stable flame front. In such case, it isnecessary to provide an ignition device capable of continuously orsemi-continuously igniting the combustible gases as they enter thereaction zone. A pilot flame or a spark producing device are exemplaryignition sources which may be employed.

In the deposition zone 728, the reacted coating precursor depositscoating 762 on the substrate 740. The remainder of the flowing streamflows from the deposition zone through a barrier zone 730 to dischargeinto the surrounding, or ambient, atmosphere. The barrier zone 730functions to prevent contamination of the deposition zone by componentsof the ambient atmosphere. The high velocity of the flowing stream as itpasses through the barrier zone 730 is a characteristic feature of thiszone. By requiring that the flowing stream achieve a velocity of atleast fifty feet per minute as it passes through the barrier zone, thepossibility of contamination of the deposition zone by components of theambient atmosphere is substantially eliminated in most coatingapplications. By requiring that the flowing stream achieve a velocity ofat least one hundred feet per minute the possibility of ambientatmosphere contamination of the deposition zone is essentiallyeliminated in those coating operations which are more highlycontamination sensitive, such as the production of TiN or WC.

In the embodiment of FIG. 7, a collar 764 is attached to and extendsperpendicularly outward from the end of conduit 760 adjacent depositionzone 728. The barrier zone 730 is defined between the collar 764 and thesubstrate 740. The collar is shaped to provide a conforming surface 766deployed close to the surface of the substrate whereby a relativelysmall clearance is provided for the exhaust of gases passing from thedeposition zone to the ambient atmosphere. The clearance establishedbetween the conforming surface 764 of the collar and the substrate issufficiently small that the exhaust gases are required to achieve thevelocity required in the barrier zone for at least a portion of theirpassage between the collar and the substrate. To this end, theconforming surface 764 of the collar 762 is shaped to lie essentiallyparallel to the surface of the substrate 740. When the surface of thesubstrate 740 is essentially planar, as it is in the illustratedembodiment, the conforming surface of the substrate is alsosubstantially planar.

Edge effects, such as elevated temperatures and residual reactivecomponents, which occur adjacent the end of the conduit 760 can extendthe deposition zone beyond the area of the substrate directly in frontof the end of conduit 760. The collar 764 should extend outward from itsjoinder to the conduit 760 a sufficient distance to preclude theback-mixing of ambient gases into the deposition zone due to a possibleVenturi effect, and to assure that the entire area of the depositionzone, as it is extended by the previously noted edge effects, isprotected from the backflow of ambient gases by the high velocityexhaust gases sweeping through the area between the collar and thesubstrate. The extended collar assures that contamination is preventedthroughout the extended deposition zone. The diameter of the collarshould be at least twice the internal diameter of conduit 760, andpreferably, should be at least five times the internal diameter ofconduit 760. The internal diameter of conduit 760 typically is in therange of 10 to 30 millimeters, and preferably is between 12 and 20millimeters.

In operation, the collar 764 is located substantially parallel to thesurface of the substrate 740 being coated and at a distance therefrom of1 centimeter or less. Preferably, the facing surfaces of the collar andthe substrate are between 2 and 5 millimeters apart. Spacing devices,such as three fixed or adjustable pins (not shown), may be provided onthe collar to assist in maintaining the proper distance between thecollar and the substrate.

The embodiment illustrated in FIG. 7 is particularly advantageous forapplying coatings to substrates which are too large, or for which it isnot convenient, to be treated in a specially controlled environment suchas a vacuum chamber or a clean room. The illustrated coating techniqueis advantageous because it can be accomplished under atmosphericpressure conditions and at more convenient “in the field” locations. Theseries of concentric conduits 722, 738, 744, 752 and 760 form a coatinghead 768 which can be supplied by relatively small flexible tubes andcan be sufficiently small to be portable. Large substrates can be coatedeither by having the coating head traverse the substrate repeatedly in araster or similar pattern, or by traversing the substrate with an arrayof coating heads arranged to cumulatively provide a uniform coating, orby rastering an array of coating heads. In addition to permitting thethin film coating of articles which previously were too large to becoated, this technique permits the coating of larger units of thosesubstrates which previously were coated under vacuum conditions.Manufacturing economies can be achieved by coating larger units of thesesubstrates, especially when mass production of the substrates isinvolved.

The embodiment illustrated in FIGS. 7 and 8 is also particularlysuitable for the production of coatings which are oxidation sensitive,such as most metal coatings. To provide such coatings the fuel is fedthrough conduit 744 in proximity to the atomized liquid media andcoating precursor, while the oxidizer is fed through conduit 752. Theatomizing gas fed through conduit 738 and/or the liquid media fedthrough conduit 722 can be materials having fuel value, they can bematerials which react with the coating precursor or they can be inertmaterials. When the produced coatings or coating precursor materials areoxygen sensitive, a reducing atmosphere is maintained in the reactionand deposition zones by assuring that the total amount of oxidizer fedis restricted to an amount less than that required to fully combust thefuel provided to the reaction zone, i.e. the oxidizer is provided inless than stoichiometric amount. Generally, the fuel excess is limitedso as to limit any flame zone which develops when the residual hot gasesmix with atmospheric oxygen. When the produced coatings and theprecursor materials are oxygen-tolerant or enhanced by the presence ofoxygen, such as in the production of most of the oxide coatings, anoxidizing or neutral atmosphere may be provided in the reaction anddeposition zones by feeding a stoichiometric or excess amount ofoxidizer. Further, with oxygen tolerant reagents and products, theoxidizer can be fed through the inner conduit 744 while fuel is fedthrough outer conduit 752.

The inert gas supplied through conduit 760 must be sufficient to shieldthe inside surface of the conduit from the reactive gases produced inthe reaction zone, and it must be sufficient, when added with the othergases from the reaction zone, to provide the gas velocity required inthe barrier zone.

The energy input can be accomplished by mechanisms other than thecombustion method illustrated in FIGS. 7 and 8. For instance, it couldbe accomplished by passing electrical current through conduit 722 tocreate electrical resistance heat in the conduit which then transfers tothe liquid medium and coating precursor as it passes through theconduit. It should be apparent that all of the conduits 722, 738, 744,752 and 760 are not required when the energy input is accomplished byother than the combustion method. Usually one or both of conduits 744and 752 are omitted when the energy input is provided by one of theelectrically derived energy input mechanisms.

The porosity or density of the deposited coating can be modified byvarying the distance between the flame zone and the deposition zone atthe substrate's surface. Generally, shortening of this distance providesan increased coating density, while increasing the distance provides amore porous coating.

In the illustrated CACCVD technique the reaction zone is generallycoextensive with the flame produced by the burning fuel. Of course, theflame zone and the substrate must be maintained sufficiently far apartthat the substrate is not damaged by the higher temperatures which wouldresult as the flame zone more closely approaches the substrate surface.While substrate temperature sensitivity varies from one substratematerial to the next, the temperature in the deposition zone at thesubstrate surface, typically, is at least 600° C. cooler than themaximum flame temperature.

When some of the alternate methods are used to supply the energy input,such as when the principal energy input is a preheated fluid which ismixed with the flowing stream in, or before it reaches, the reactionzone, the maximum temperatures produced in the reaction zone aresubstantially lower than those produced with a combustion energy input.In such cases the coating properties can be adjusted by varying thedistance between the reaction zone and at the substrate surface withless concern for overheating the substrate. Accordingly, the termsreaction zone and deposition zone are useful in defining functionalregions of the apparatus but are not intended to define mutuallyexclusive regions, i.e. in some applications reaction of the coatingprecursor may occur in the deposition zone at the substrate surface.

The lower maximum temperatures resulting when the principal energy inputis other than a combustion flame enables the use of temperaturesensitive coating materials, such as some organic materials. Inparticular, polymers may be deposited as protective coatings or asdielectric interlayer materials in capacitors, integrated circuits ormicroprocessors. For instance, a polyamide coating could be providedfrom its polygamic acid precursor. Similarly, polytetrafloroethylenecoatings could be provided from low molecular weight precursors.

The energy input to the flowing stream prior to its leaving the reactionzone generally negates the need to provide energy to the deposition zoneby heating the substrate, as is often required in other coatingtechniques. In the present deposition system, since the substrate actsas a heat sink to cool the gases present in the deposition zone, ratherthan heating them, the temperatures to which the substrates aresubjected are substantially less than are encountered in systems whichrequire that energy be transmitted to the deposition zone through thesubstrate. Accordingly, the CACCVD coating process can be applied tomany temperature sensitive substrate materials which can not be coatedby techniques which involve heating through the substrate.

A wide range of precursors can be used as gas, vapor or solutions. It ispreferred to use the lowest cost precursor which yields the desiredmorphology. Suitable chemical precursors, not meant to be limiting, fordepositing various metals or metalloids are as follows:

Pt platinum-acetylacetonate [Pt(CH₃COCHCOCH₃)₂] (in toluene/ methanol),platinum-(HFAC₂), diphenyl-(1,5-cyclooctadiene) Platinum (II). [Pt(COD)in toluenepropane] platinum nitrate (in aqueous ammonium hydroxidesolution) Mg Magnesium naphthenate, magnesium 2-ethylhexanoate[Ma(OOCCH(C₂H₅)C₄H₉)₂], magnesium naphthenate, Mg-TMHD, Mg-acac,Mg-nitrate, Mg-2,4-pentadionate Si tetraethoxysilane [Si(OC₂H₅)₄],tetramethylsilane, disilicic acid, metasilicic acid P triethyl phosphate[C₂H₅O)₃PO₄], triethyllphosphite, triphenyl phosphite La lanthanum2-ethylhexanoate [La(OOCCH(C₂H₅)C₄H₉)₃] lanthanum nitrate [La(NO₃)₃],La-acac, La-isopropoxide, tris (2,2,6,6-tetramethyl-3,5-heptanedionato), lanthanum [La(C₁₁H₁₉O₂)₃] Cr chromiumnitrate [Cr(NO₃)₃], chromium 2-ethylhexanoate [Cr(OOCCH(C₂H₅)C₄H₉)₃],Cr-sulfate, chromium carbonyl, chromium (III) acetylacetonate Ni nickelnitrate [Ni(NO₃)₂] (in aqueous ammonium hydroxide), Ni-acetylacetonate,Ni-2-ethylhexanoate, Ni-napthenol, Ni-dicarbonyl Al aluminum nitrate[Al(NO₃)₃], aluminum acetylacetonate [Al(CH₃COCHCOCH₃)₃], triethylaluminum, Al-s-butoxide, Al-i- propoxide, Al-2-ethylhexanoate Pb Lead2-ethylhexanoate [Pb(OOCCH(C₂H₅)C₄H₉)₂], lead naphthenate, Pb-TMHD,Pb-nitrate Zr zirconium 2-ethylhexanoate [Zr(OOCCH(C₂H₅)C₄H₉)₄],zirconium n- butoxide, zirconium (HFAC₂), Zr-acetylacetonate,Zr-n-propanol, Zr-nitrate Ba barium 2-ethylhexanoate[Ba(OOCCH(C₂H₅)C₄H₉)₂], Ba-nitrate, Ba-acetylacetonate, Ba-TMHD Nbniobium ethoxide, tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)niobium Ti titanium (IV) i-propoxide [Ti(OCH(CH₃)₂)₄], titanium (IV)acetyl- acetonate, titanium-di-i-propoxide-bis-acetylacetonate,Ti-n-butoxide, Ti-2-ethylhexanoate, Ti-oxide bis(acetylacetonate) Yyttrium 2-ethylhexanoate [Y(OOCCH(C₂H₅)C₄H₉)₃], Y-nitrate,Y-i-propoxide, Y-napthenoate Sr strontium nitrate [Sr(NO₃)₂], strontium2-ethylhexanoate, Sr(TMHD) Co cobalt naphthenate, Co-carbonyl,Co-nitrate, Au chlorotriethylphosphine gold (I),chlorotriphenylphosphine gold(I) B trimethylborate, B-trimethoxyboroxineK potassium ethoxide, potassium t-butoxide, potassium 2,2,6,6-tetramethylheptane-3,5-dionate Na sodium2,2,6,6-tetramethylheptane-3,5-dionate, sodium ethoxide, sodiumt-butoxide Li lithium 2,2,6,6-tetramethylheptane-3,5-dionate, lithiumethoxide lithium-t-butoxide Cu Cu(2-ethylhexonate)₂, Cu-nitrate,Cu-acetylacetonate Pd paladium nitrate (in aqueous ammonium hydroxidesolution) (NH₄)₂Pd(NO₂)₂, Pd-acetylacetonate, ammonium hexochloro-palladium Ir H₂IrCl₆ (in 50% ethanol in water solution),Ir-acetylacetonate, Ir-carbonyl Ag silver nitrate (in water), silvernitrate, silver fluoroacetic acid, silver acetateAg-cyclohexanebutyrate, Ag-2-ethylhexanoate Cd cadmium nitrate (inwater), Cd-2-ethylhexanoate Nb niobium (2-ethylhexanoate) Mo(NH₄)₆Mo₇O₂₄, Mo(CO)₆, Mo-dioxide bis (acetylacetonate) FeFe(NO₃)₃.9H₂O, Fe-acetylacetonate Sn SnCl₂.2H₂O, Sn-2-ethylhexanoate,Sn-tetra-n-butyltin, Sn- metramethyl In In(NO₃)₃′ × H₂O,In-acetylacetonate Bi Bismuth nitrate, Bismuth 2-ethyl hexonate RuRu-acetylacetonate Zn Zn-2-ethyl hexonate, Zn nitrate, Zn acetate WW-hexacarbonyl, W-hexafluoride, tungstic acid Ce Ce-2-ethyl hexonate

In most cases where a mixture of metal precursors and/or metalloidprecursors are deposited, the deposition is generally stoichiometricwith respect to the relative proportions of the metal(s) and/ormetalloid(s) provided by the precursors in the reaction mixtures.However, this relationship is neither precise nor entirely predictable.Nevertheless, this does not present any significant problem in achievinga coating layer or powder of desired composition because the relativeamounts of chemical precursors required to obtain a coating layer orpowder of desired composition can be readily determined without undueexperimentation for any set of coating parameters. Once a ratio ofchemical precursors under a set of coating parameters is determined toobtain a coating or powder of desired composition, the coating can beduplicated with highly predictable results. Thus, if one desired acoating or powder that would contain two metals in a particularpredetermined ratio, one might start out with two chemical precursorscontaining the two metals in the predetermined stoichiometric ratio. Ifdetermined that the two metals were not deposited in the predeterminedratio, adjustments would be made in the relative amounts of the twoprecursor chemicals until the desired ratio of metals in the depositedmaterials was achieved. This empirical determination would then berelied upon for future depositions.

CCVD has the advantages of being able to deposit very thin, uniformlayers which may serve as the dielectric layers of embedded capacitorsand resistors. For embedded capacitors, the deposited dielectric layersare typically between about 0.03 and about 2 microns thick, preferablybetween about 0.1 and about 1 micron thick and most preferably betweenabout 0.2 and about 0.6 microns thick. The material can be deposited toany desired thickness; however, for forming layers by CCVD or CACCVD,thicknesses seldom exceed 5 microns. Because the thinner the dielectriclayer, the higher the capacitance, the ability to deposit very thinfilms is an advantageous feature of the CCVD process. The thinness ofthe metallic coating which may be deposited as part of the capacitorstructure also facilitates rapid etching.

Examples of coatings produced by CCVD include silicon dioxide coatingsproduced from a solution of tetraethoxysilane [Si(OC₂H₅)₄] inisopropanol and propane; platinum coatings produced from a solution ofplatinum-acetylacetonate [Pt(CH₃COCHCOCH₃)₂] in toluene and methanol;and nickel-doped LaCrO₃ coatings produced from solutions of lanthanumnitrate in ethanol, chromium nitrate in ethanol and nickel nitrate inethanol.

This invention is directed to thin film capacitor structures, andcertain such structures will now be described in reference to FIGS. 4-6,although it is to be understood that these structures are not to beconsidered encompassing of possible thin layer capacitor structures towhich the present invention is directed. The thin film capacitorstructures described herein for embedding in printed circuitry, and theunsupported capacitor structures must have some flexibility. Thisdistinguishes capacitor structures produced for the semiconductorindustry on silicon wafers which are rigid structures. Herein,“flexible” when used in respect to capacitor structures and parts ofcapacitor structures, e.g., metal foils, dielectric layers, etc., meanscapable of being bent around a 6-inch radius without damage ordestruction.

FIG. 4A is directed to a three-layer structure 400. On a flexible metalfoil 402 is deposited, e.g., by CCVD or CACCVD, a dielectric materiallayer 402, and on the dielectric material layer 404 is deposited a metallayer 406. The metal layer 406 may be deposited entirely by CCVD orCACCVD, or a very thin (0.005 to 0.1 micron) seed layer of metal (e.g.,platinum) deposited and additional metal, (e.g., Cu, Ni or Zn) depositedby electroplating to a desired thickness. Generally, a sufficient seedlayer is deposited when the electrical resistance between two surfacecontact points is 1 megohm or less. The metal foil 402 is typicallybetween about 12 and about 110 microns thick. The deposited metal layer406 is electrically functional at about 0.1 microns, although forstructural integrity this layer will typically be 0.5 to 3 micronsthick, or even thicker if desired. The structure of FIG. 4A is, initself, a capacitor, and may be used as such in a printed circuit boardas a decoupling capacitor to help maintain square electrical signals.

In FIG. 4B, the deposited metal layer 406 of FIG. 4A has been patternedby photoresist imaging and etching to produce discrete patches 408 ofmetal. In this structure, the foil 402 serves as a common electricalconductive capacitor plate, the dielectric layer 404 serving as a commondielectric layer, and multiple discrete capacitor plates are provided bythe discrete patches of metal opposed to the common plate. In caseswhere it is undesirable that a common plate serve for all opposeddiscrete capacitor plates, the foil 402 can be similarly patterned intodiscrete capacitor plates by a photoresist/etching process. If so, afterthe deposited metal layer 406 is patterned into discrete plates 408,this side of the structure is laminated to the epoxy resin layer 410prior to photoresist/etching processing of the foil layer, whereby thelaminated resin 410 provides support for the structure after the foil402 is patterned. Then, the foil side is also laminated with anotherepoxy resin layer 410 to produce an embedded structure. A structure inwhich the Foil layer is patterned into discrete plates 409 is shown inFIG. 4C.

In embedded layers, the plates are conventionally connected toelectronic circuitry by plated via holes (not shown).

FIG. 5A is a capacitor structure 500 in which successive deposition oflayers is on a polymeric support sheet 501. A metal layer 502, e.g.,nickel or copper, is deposited by CACCVD on a polyamide sheet; adielectric layer 504 is deposited thereon; and a second metal layer 506is then deposited by CCVD, CACCVD or by electroplating. The structure500 is a capacitor and may serve in this form as a decoupling capacitorin the manner of the structure 400 of FIG. 4A. The final metal layer 506can be patterned to produce the discrete capacitor plates 508 of FIG. 5Bin a photoresist/etching process. The capacitor structure 500, either asshown in FIG. 5A as a decoupling capacitor or with a patterned metallayer providing discrete capacitor plates 508 on one side of thestructure, is generally embedded in epoxy resin. A second capacitorstructure could also be formed on the other side of the polymericsupport sheet 501 by successively depositing a metal layer, a dielectriclayer and another metal layer. In such a structure, the metal layers502, 506 are each between about 0.5 and about 3 microns thick and thedielectric layer 504 between the metal layers is between about 0.03 andabout 2 microns thick.

In FIG. 6, a five-layer structure 600 is formed including a flexiblefoil 602, a barrier layer 603 that serves as a heat barrier to preventthe foil layer from melting or from oxidation and/or a diffusion barrierto prevent chemical interaction between the foil layer and thedielectric material layer, a dielectric layer 604, an adhesion layer605, and a deposited metal layer 606. The functions and compositions ofthe barrier layer 603 and of the adhesion layer 605 are to be discussedin greater detail hereinafter.

An important class of dielectric material layers which may be depositedby CCVD in accordance with the invention are silica and silica-basedcompositions, including 100% silica layers, amorphous and crystalline,but also doped silica and silica mixed with other oxides, such as PbO,Na₂O, Li₂O, K₂O, Al₂O₃, and B₂O₃. Herein, silica-based compositions aredefined as dielectric materials having from about 1%, preferably atleast about 3 wt %, more preferably at least about 20 wt % up to 100 wt% silica. Generally, silica comprises at least about 10 mole percent,preferably at least 40 mole percent up to 100 mole percent of asilica-based composition. The reason why compositions may be considered“silica-based composition” having very low weight percentages of silicais that many of the oxides, such as lead oxide, with which the silicamay be co-deposited have high molecular weights compared to silica.

Some silica-based compositions deposited as dielectric materials are setforth in the following table.

Dielectric Compositions Component Composition of Fraction (wt %)Amorphous Silica SiO₂ SiO₂ 100 Lead Silicate (with SiO₂ 41 27.4 51.1 3 563 56 42 lithium, sodium, potassium, PbO 52.3 62.8 48.9 75 82 22 29 49aluminum, and boron) Na₂O 5.2 2.1 — — — 7 4 2 Li₂O 1.3 0.7 — — — — — 1K₂O 14.1 7.0 — — — 7 9 6 Al₂O₃ — — — 11 3 1 2 — B₂O₃ — — — 11 10 — — —Doped silica SiO₂ Dopants Dopant amounts vary according the degree (Pt,B, Ba, Ca, of doping Mg, Zn etc.)

The dielectric layer may have layers of different composition. Forexample, a multi-layer film can be of alternating layers of silica andlead silicate, a dual layer comprising a lead silicate base with a topcoat of lead aluminum boron silicate, or a compositely gradient film ofsilica to doped silica to lead silica. The multi layers may be depositedby varying the content of the precursor solution which is fed to theflame or by moving the substrate to successive deposition stations wherelayers of different composition are deposited.

Dielectric materials in accordance with the invention may be doped witha variety of elements, such as Pt, B, Ba, Ca, Mg, Zn, Li, Na, K, etc.The dopants will affect the dielectric value of the dielectric layer.Generally a material is considered a dopant if it is present at up toabout 25 wt % of the dielectric, e.g., silica-based glass, typically nomore than about 5 wt %.

Some other dielectric materials which may be deposited by CCVD include,but are not limited to BST, SrTiO₃, Ta₂O₅, TiO₂, MnO₂, Y₂O₃, SnO₂, andPLZT.

A material particularly suitable as a dielectric material for thin filmcapacitors is barium titanium oxide (Ba₂Ti₉O₂₀) and zirconium-dopedbarium titanium oxide (Ba₂Ti_(1−(9−x))Zr_(x−8)O₂₀); x>0). To function asdielectric layers, these materials preferably are deposited incrystalline form. Barium titanium oxide has been used as a microwaveceramic material in bulk form for wireless communication. It is believedthat use of these materials as a dielectric for thin film capacitors isunique. Zirconium-doped barium titanium oxide can provide a high qualityfactor, e.g., 14000 at 3 Ghz, and a dielectric constant of about 40.Also, zirconium has a wide range of temperature coefficient of resonancefrequency (0-9 ppm/° C.) in telecommunication applications. Thesematerials are low loss, reducing consumption of electrical energy andgeneration of thermal energy. These materials have high permittivity,thereby permitting capacitors of small size to provide high capacitance.Accordingly, barium titanium oxide, particularly zirconium dopedcapacitors are ideal candidates for demanding electronics, especially inhigh frequency applications where loss is always in need of reductions.

Tin-doped barium titanium oxide (Ba₂T_(1−(9−x))Sn_(x−8)O₂₀; x>0) canalso be used, but is less preferred relative to the zirconium-dopedcounterpart.

All of these materials can be deposited a thin layers on a substrate bythe CCVD process by appropriate selection of precursors in the precursorsolution.

The dielectric layer acts to prevent the flow of electrons between thecapacitor plates, whereby a charge may be built up on between theplates. However, is some cases, a certain amount of leakage is desiredbetween the plates, particularly in decoupling capacitors, such as maybe formed with the structure of FIG. 4A. Glasses, including, but notlimited to silica glass and lead silica glass, may be doped with singlevalent cations, such as Na⁺, K⁺, Li⁺, Ag⁺, etc. functioning as ionicconductors. The amount of doping required to achieve the desired degreeof lossy-ness will vary upon a variety of factors, including theparticular dielectric used, the thickness etc. Also a thinner layer canbe deposited to increase capacitance and loss. These layer should befrom 0.05 to 0.3 μm thick. Generally lossy dielectrics will have anelectrical conductivity value of from about 10⁻¹ to about 10⁻⁵ amperesper cm².

If metal foil is the substrate upon which the dielectric layer isdeposited, e.g., as discussed above in reference to FIG. 4A, the mostcommon choice is copper foil. Most electronic circuitry utilizes copperas the primary conductive element.

However, in accordance with the invention, alternative conductivemetals, particularly metal foils, as substrates for dielectric layerdeposition are herein suggested. Copper melts at 1083° C.; thus,deposition on copper is limited to materials which can be deposited byCCVD at lower temperatures. Accordingly, materials which must bedeposited at temperatures upwards of about 1000° C. cannot be depositedon copper, but must be deposited on a substrate which melts at a highertemperature.

Proposed metal substrates for higher temperature CCVD applications havemelting points upward of about 1350° C. so as to withstand higherdeposition temperatures required for certain materials to be depositedby CCVD. Barium strontium titanate (BST) is an example of a dielectricmaterial which cannot be deposited on copper and crystallize to thedesired material. To obtain the desired crystalline structure, BST mustbe deposited at higher temperatures, such as the deposition temperatureswhich the substrates of the present invention can be deposited. Examplesof other materials which are not suitable for deposition on copper byCCVD, but which may be deposited on the substrates of the presentinvention, include, but are not limited to oxide and mixed oxide phaseswhich contain Ti, Ta, Nb, Zr, W, Mo or Sn.

Furthermore, copper has a relatively high coefficient of linear thermalexpansion, typically considerably higher than many of the proposeddielectric material layers, particularly oxides, that would be depositedthereon. If there is a substantial mismatch in coefficients of thermalexpansion between the substrate and the CCVD-deposited film, the filmthat was deposited at high temperature may crack as the coated substratefilm cools. Preferably, metal substrates for CCVD deposition havecoefficients of linear thermal expansion below about 15 ppm/° C.⁻¹, morepreferably below about 12 ppm° C.⁻¹. To avoid thermal cracking of thefilm, the coefficient of linear thermal expansion of the substrateshould be no more than about 80% above that of the material to bedeposited, preferably no more than about 40% above that of the materialto be deposited and most preferably no more than about 20% above that ofthe material to be deposited. The closer the coefficient of thermalexpansion, the thicker the material the coating material can bedeposited and/or the higher the deposition temperature may be withoutcracking of the coating.

Specific metals and alloys e.q., as foils, which serve ashigh-temperature or low thermal expansion substrates in accordance withthe invention include nickel, tungsten, iron, niobium, molybdenum,titanium, nickel/chromium alloy, and iron/nickel/chromium alloy, such asthat sold under the trademark Inconel®. In the nickel/chromium and ironnickel chromium alloys, iron is present at between 0 and about 25 wt %,nickel between about 50 and about 80 wt %, and chromium between about 10and about 30 wt %. If iron is present, it is typically present at least2 wt %.

These metals have low thermal expansion, which will be needed withproposed future PWB dielectric polymer materials such as liquidcrystals, and also have low thermal conductivity. A low thermalexpansion printed wiring board (PWB) will have easier interconnectionwith silicon based direct attached chips (less strain during thermalchanges). These materials are important because they are a close matchto liquid crystal polymers' thermal expansion, low or moderate in price,are etchable, solderable, and have good or reasonable thermal andelectrical conductivities. Except for iron all form more protectiveoxides than Cu. Another thermal expansion consideration is the coatingmaterial, which may be applied to form materials for such applicationsas resistor, capacitors and inductors. All of these materials are closerin thermal expansion to oxides for dielectric applications, and canwithstand higher temperature than copper, which is currently used forembedded devices, hence enabling the depositions of higher temperaturedielectric or ferroelectric materials such as barium strontium titanateand lead lanthanum zirconium titanate.

Copper has a melting point of 1083° C. The higher melting point of thesemetals enable the depositions of various materials not depositable oncopper and the lower thermal expansion prevents the film cracking due tothe thermal expansion mismatch. Furthermore, the oxides formed on thesemetal surfaces are less oxygen permeable than copper oxide and henceimpede further oxidation to the bulk metals. Some selected physicalproperties are listed in the following table for thisinvention-suggested metals along with the comparison with copper.

W Mo Nb Ingot Iron Liquid crystal Ni Copper Thermal expansion, 10⁶/° C.4.5 4.8 7.3 11.7 5 13.3 16.5 Electrical resistively, μΩcm 5.6 43 15.29.7 dielectric 10 1.7 Thermal Conductivity, W/cm ° C. 1.74 1.38 0.5370.82 Approx. 0 0.907 4.01 Melting point ° C. 3422 2623 2477 1540 Approx.0 1440 1080

If copper foil, or another metal foil with similar low meltingtemperature and/or oxide-forming tendencies, is the foil substrate ofchoice, FIG. 6 discussed above illustrates a five-layer structurecomprising a metal foil layer 602, a barrier layer 603, a dielectriclayer 604, an adhesion-promoting layer 605 and a deposited metal layer606. The barrier layer 603 is a CCVD-deposited layer of a material,e.g., Tungsten oxide (WO₃), Strontium oxide (SrO), mixed tungstenstrontium oxides, such as SrWO₄, BaWO₄, CeO₂, Sr_(1−x)Ba_(x)WO₄, SiO₂,Cr₂O₃, Al₂O₃, Ni, Pt and very thin multilayers of these, which can bedeposited at a sufficiently low temperature that neither melting noroxidation of the metal foil layer is a problem. Subsequently, adielectric layer 604 may be deposited at a higher temperature than wouldbe acceptable on the bare surface of the foil 602. The barrier layer 603is generally thin, i.e., between about 0.01 and about 0.08 micron thick.

Tungsten oxide (WO₃), Strontium oxide (SrO), mixed tungsten strontiumoxides, such as SrWO₄, BaWO₄, CeO₂, Sr_(1−x)Ba_(x)WO₄, mentioned aboveas suitable barrier layer material may also serve as materials forforming a dielectric layer. These dielectric materials are particularlyadvantageous as dielectric materials for deposition on substrates whichcannot withstand the higher deposition temperatures of other dielectricmaterials which may be deposited by CCVD. These materials can bedeposited as dense, adherent coatings at temperatures of about 700° orbelow gas temperature, the substrate temperature during deposition beinggenerally about 200 to 500° lower. Suitable substrates on which thesedielectric materials may be deposited include, but are not limited tocopper, aluminum and polyimide.

Depositing the dielectric layer at low temperatures reduces the effectof thermal expansion mismatch and the potential of oxidizing the saidmetal substrates and deforming/degrading the said plastic substrate.Unlike these materials, i.e., WO₃, SrO, mixed tungsten strontium oxides,such as SrWO₄, BaWO₄, CeO₂, Sr_(1−x)Ba_(x)WO₄, most other highpermittivity dielectric materials generally require higher depositiontemperatures and thus, a low temperature barrier layer, such as a lowtemperature SiO₂ coating has to be applied prior to the deposition ofthe high permittivity materials to protect the substrate from oxidation.However, silica does not have a very high dielectric constant, comparedto most other dielectrics, and therefore, the overall capacitance isreduced. In contrast, all of these low deposition temperature dielectricmaterials have higher dielectric constants than silica and thus, theycan also be deposited as base coatings to protect the substrate withoutsignificantly reducing the capacitance. Higher temperature materialswith even higher permittivity can then be coated to achieve an evenhigher capacitance. Using combustion chemical vapor deposition (CCVD),the materials can be deposited in thin film form and integrated intoprinted circuit boards (PCB).

In some cases, adhesion problems have been experienced between (withreference to FIG. 6) the dielectric material of layer 604 and thedeposited metal layer 606. For example, adhesion problems have beenexhibited between a deposited silica layer and a deposited platinumlayer. In such case, an adhesion (or interfacial) layer 605 may bedeposited. For example, a layer 605 of chromia has been found to promoteadhesion between platinum and silica. The adhesion layer may be aconductive oxide, such as zinc oxide. The adhesion layer 605 may also bea functionally gradient material (FGM) layer in which the composition ofthe layer changes throughout the layer. For example, silica-to-platinumadhesion may be promoted by a silica/platinum adhesion layer 605 whichchanges incrementally or continuously in composition from high silicacontent at the silica side to high platinum content at the platinumside. Deposition of functionally gradient material layers is possibleusing CCVD by either continuously changing the content of the precursorsolution during deposition or depositing the layer at several stationsalong a coating line. In general, a material, which contains elements incommon with the two layers between which it is interposed, acts topromote adhesion. The adhesion layer 605 is likewise typically quitethin, i.e., between about 0.001 and about 0.05 micron thick.

If a conductive oxide is used as the adhesion layer 605, it is possibleto use such layer as a seed layer for electroplating, e.g., of copper,nickel or zinc. Zinc oxide, for example can be used as a seed layer forelectroplating of zinc, whereby excellent adhesion is realized by anoxide dielectric layer and the plated zinc layer.

While FIG. 6 shows a structure with both a barrier layer 603 between thefoil 602 and the dielectric layer 604 and an adhesion layer 605 betweenthe dielectric layer 604 and the deposited metal layer 606, it is to beunderstood that a capacitor structure may contain only a barrier layer603 or only an adhesion layer 605 as is necessitated by constructionconstraints.

Alternatively it may be necessary to provide adhesion and barrier layeron both side of the dielectric.

Among other factors, capacitance of a capacitor in accordance with thisinvention is a function of the surface area of the dielectric material.Accordingly, increasing the surface area at the interface of thedielectric material layer and the metal, e.g. metal foil, on which it isdeposited and increasing the surface area at the interface of thedielectric layer and a metal layer deposited thereon while maintainingintimate contact, increases capacitance. If a metal foil is thesubstrate, as per FIG. 4A, it is generally possible to obtain such foilswith varying degrees of surface roughness. Surfaces of foil may befurther roughened mechanically, electrically, or chemically. Thus, forexample, one might purchase a foil with a known degree ofmicro-roughness, and chemically etch to add nano-roughness. Formeaningfully increasing capacitance, it is desired that the roughness ofa metal on which a dielectric layer is to be deposited be at least 1.1,preferably at least about 2 cm²/cm². Preferably the roughness is lessthat 5 cm²/cm², due to degradation of dielectrics electrical properties.Another parameter of surface roughness is feature height, which ispreferably less that about 5 microns, more preferably less than about 2micrometers. In some cases it is desired to have features of these lessthan 0.5 micrometers.

Because of the thinness of the dielectric layer that is deposited, it ismore difficult to roughen the surface, although some chemical rougheningmay be done chemically. Roughness also improves adhesives in PWB. If torough, then the dielectric can not be made continuous and somecapacitors are shorted. Surface roughening of the dielectric materiallayer may best be achieved by adjusting its deposition conditions so asto deposit a layer with a rough exposed surface. Various factors, suchas deposition temperature, may affect the roughness of the dielectricmaterial layer surface; however, the most significant factor affectingsurface roughness of the dielectric material layer appears to bedeposition rate. As a rule of thumb, if one were to obtain a set ofdeposition parameters for optimal smoothness at highest deposition rate,and then double or triple that deposition rate, one would obtain a roughsurface. Preferably the surface of the deposited dielectric material isat least about 1.2 cm²/cm², preferably at least 2.6 cm²/cm². Preferablythe roughness is less that 20 cm²/cm², due to degradation of dielectricselectrical properties. Preferably the feature height of the dielectricrelative to the substrate surface is less than 2 microns, preferably atleast about 1 micron. The surface area should be increased at least 10%and preferably at least 30%, in some cases it is desired to be increasedat least 60%, compared to the substrate prior to any dielectricdeposition.

One of the most important metals which can be deposited as a metallayer, such as layer 406 in FIG. 4A, in doped or undoped form by CACCVD,is nickel. Nickel is inexpensive and can be selectively etched relativeto other conductive metals, such as copper. An important precursor fordepositing zero valence nickel by CACCVD is nickel nitrate. Nickel maybe deposited from an ammoniacal aqueous solution of nickel nitrate.However, as described above, it is preferred that deposition be from aliquid at conditions approaching supercritical. To this end,advantageous carriers for nickel nitrate include liquefied ammonia orliquefied nitrous oxide (N₂O). Nitrous oxide may be liquefied bypressurizing to 700-800 psi. Ammonia may be liquefied by pressurizationand/or low temperatures. Whether the carrier is liquefied ammonia orliquefied nitrous oxide, it is found advantageous to add a minor portionof water, i.e., up to about 40 wt %, preferably between about 2 to about20 wt %, (the liquefied ammonia or liquefied nitrous oxide comprisingthe balance, between about 60 and about 100 wt %). The water raises thesupercritical point of either liquefied ammonia or liquefied nitrousoxide. This makes it easier to operate sufficiently below thesupercritical point such that variations in viscosity and density arenot encountered. Also, the addition of water reduces the instability ofthe solutions. (It is to be understood, however, that depositions may,in some cases, be carried out in liquified ammonia or liquefied nitrousoxide without the addition of water.) In such nickel depositionsolutions, the nickel precursor along with any precursor for a nickeldopant are typically present at a low level, i.e., from about 0.001 wt %to about 2.5 wt %. Currently preferred dopants for nickel are nickelphosphorous and/or nickel phosphorous oxides, e.g., nickel phosphate. Itis believed that when using a phosphorus-containing precursor, such asphosphoric acid, the major dopant species is nickel phosphate. Precursorsolutions in which water and either liquefied ammonia or N₂O are thecarrier co-solvents are advantageous in that no carbon is present whichcould result in deposition of carbon.

When preparing a precursor solution of nickel nitrate to be carried inliquefied ammonia, the nickel nitrate may be conveniently pre-dissolvedin ammonium hydroxide solution along with precursor for any dopant, andthis solution then admixed with liquefied ammonia.

As noted above, there may be instances where it is desirable to etch asilica or silica-based dielectric layer. Suitable etchants for silicaand silica-based compositions include ammonium hydrogen difluoride,fluoroboric acid and mixtures thereof. One particularly suitable etchantfor silica and silica-based compositions is an aqueous solution of 1.7wt % ammonium hydrogen difluoride, and 1.05 wt % fluoroboric acid. Othermaterials can be added to a mixture of these two components.

The invention will now be described in greater detail by way of specificexamples.

EXAMPLE 1

One sample was prepared to evaluate the electrical properties of thesilica film using I-V and C-V measurements. The film consisted ofamorphous silica (100% SiO₂) with a thickness of 0.25 mm and wasdeposited on Si/Ti/Pt wafer. The deposition was accomplished by usingcombustion chemical vapor deposition (CCVD). The precursor solutionconsisted of 0.873 wt % tetraethyloxysilane, 7.76 wt % isopropyl alcoholand 91.4 wt % propane. The solution was then nebulized by nearsupercritical atomizer into a flame. The flame was directed at the waferand the deposition was completed in 10 minutes.

To provide a top electrodes, aluminum dots of 500 nm thickness weredeposited by masking e-beam technique. The aluminum dots were of twodiameters; 1.5 mm and 0.7 mm. The individual dot then act as acapacitor. The capacitors were characterized by HP4280A 1 MHz C meterfor C-V measurement and HP4010A I-V pA meter for IV. Generally, theleakage current density of 1-3 nA/cm² was measured at the electric fieldof 0.5 MV/cm. The average breakdown voltage measured for the capacitors(dots) of 1.5 mm diameter was 74.3 V, and every capacitor showedbreakdown. For capacitors of 0.7 mm diameter, five out of the elevencapacitors sustained up to 100 V bias and the average breakdown voltagewas 80 V. The average breakdown filed strength of films were 2.9 to 3.2MV/cm. These capacitor area dependence showed that the breakdown valuesdepend on not only the intrinsic properties of the dielectric films butalso the number of flaws in the films. When a breakdown voltage of above100V bias was measured, this indicated that the breakdown field strengthof the silica film was over 4MV/cm.

The capacitance density (nF/cm2) of the silica dielectric films were20.01-20.69 nF/cm². The electrical measurement is summarized in thefollowing table.

Capacitor Size, x10⁻³ cm² 17.67 4.42 Capacitance Density, nF/cm² 20.0120.69 Leakage Current Density, nA/cm² 1.24 3.12 Breakdown Voltage, V74.3 80.0 Breakdown Field, MV/cm 2.97 3.2

EXAMPLE 2

A silica film of 0.07 μm (at edge) to 0.14 μm (at center) thickness wasdeposited on Cu foil via CCVD processing. The film was deposited usingthe same precursor solution and by the same process as described inExample 1. The deposition was accomplished in 9 minutes.

The aluminum top electrodes of 0.50 μm thickness were applied by e-beammasking technique and the Cu foil substrate served as a groundelectrode. The C-V measurement instrument was HP4280A 1 MHz C meter andthe I-V measurement was done by HP4010A I-V pA meter. Measurements wereonly performed at the area of 0.07 and 0.15 μm thickness and the resultsare summarized in the following table.

Capacitance Density, nF/cm² Film Number of Standard Maximum MinimumThickness Sample Average Deviation Value Value 1500A  9 63.6 3.6 68.356.7 700A 11 85.3 6.2 97.1 76.2

EXAMPLE 3

A silica film of unknown thickness (but was estimated from thedeposition time to be half the thickness of the sample in Example 2) wasdeposited on Ni foil via CCVD processing. The film was deposited usingthe same precursor solution and by the same process as described inExample 1. The deposition time was 5 minutes.

The aluminum top electrodes of 0.5 μm thickness were applied by e-beammasking technique and the Ni foil substrate served as a groundelectrode. The C-V measurement instrument was HP4280A 1 MHz C meter andthe I-V measurement was done by HP4010A I-V pA meter. The results aresummarized in the following table.

Number of Aver- Standard Maximum Minimum Sample age Deviation ValueValue Capacitance 15 67.83 8.94 89.5 56.5 Density, nF/cm² BreakdownVoltage 15 5.6 3.3 12 2 Dissipation Factor 15 0.106 0.022 0.124 0.098

EXAMPLE 4

Barium strontium titanate (BST) was deposited on Ni-200 shim by the CCVDprocess. The precursor solution was composed of, by weight percentage,0.79% barium bis(2-ethylhexanoate), 0.14% strontiumbis(2-ethylhexanoate), 0.23% titaniumdiisopropoxide-bis(acetylacetonate) 17.4% toluene, and 81.5% propane.The film was deposited by the same process as described in Example 1.The deposition was completed in 48 minutes.

EXAMPLE 5

Silica solution for CCVD was consisted of 0.87 wt % tetraethyloxysilane,7.76 wt % isopropyl alcohol, and 91.37 wt % propane. The mixingprocedure for preparing Pt solution is as follows: platinum (II)acetylacetonate (0.33 wt %) and toluene (19.30 wt %) were ultrasonicallymixed for 5 min before the addition of methanal (80.40 wt %). SiO₂—Ptwere prepared in the following way: Ultrasonically mixedtetraethyloxysilane (0.38 wt %), isopropyl alcohol (2.02 wt %), platinum(II) acetylacetonate (0.30 wt %), and toluene (17.90 wt %) for 5 minutesand then added methanal (79.40 wt %). Thin films were deposited as thesubstrate moved across the flame of the combusted precursor solutions.Multilayers of silica, silica-platinum composite, and platinum weredeposited in that order; the Pt—SiO₂ was coated to act as an interfaciallayer for adhesion improvement which is currently being investigation.

EXAMPLE 6

Silica solution for CCVD was consisted of 0.87 wt % tetraethyloxysilane,7.76 wt % isopropyl alcohol, and 91.37 wt % propane. Chromia solutionwas composed of 0.10 wt % chromium (III) acetylacetonate, 14.60 wt %toluene, 5.70 wt % 1-butanol, and 79.60 wt % propane. Pt solution wasprepared in the following way: platinum (II) acetylacetonate (0.33 wt %)and toluene (19.30 wt %) were ultrasonically mixed for 5 min before theaddition of methanol (80.37 wt %). Silica (base layer), Chromia(interfacial layer), and platinum (electrode) thin films were depositedas copper substrate (TC/TC) moved across the flame of the combustedprecursor solutions. The specimen was then electroplated with copper andsubject to peeling test.

EXAMPLE 7

Silica solutions for CCVD were consisted of (1) 0.87 wt %tetraethyloxysilane, 7.76 wt % isopropyl alcohol, and 91.37 wt %propane, (2) 1.73 wt % tetraethyloxysilane, 7.69 wt % isopropyl alcohol,and 90.58 wt % propane, and (3) 2.57 wt % tetraethyloxysilane, 7.63 wt %isopropyl alcohol, and 89.8 wt % propane. Thin films were deposited assubstrate moved across the flame of the combusted precursor solutions.Under scanning electron microscope, surface roughness increased withincreasing concentration of tetraethyloxysilane.

EXAMPLE 8

Silica solution for CCVD was consisted of 0.87 wt % tetraethyloxysilane,7.76 wt % isopropyl alcohol, and 91.37 wt % propane. Thin films weredeposited as substrate moved across the flame of the combusted precursorsolutions. The capacitance increased from 16.0 nF in a capacitor with aslower feed rate (3 ml/min) to 39.6 nF in a capacitor with a higher feedrate (5 ml/min) due to surface roughening.

EXAMPLE 9

Silica (SiO₂) was deposited via CCVD processing (from TEOS,tetraethoxysilane, in ISP, isopropanol) as a base layer onto thesuperalloy MAR-M247 prior to the deposition of alumina (Al₂O₃) (fromaluminum acetylacetonate). The silica was deposited initially at atemperature 200 to 300° C. less than that of the alumina. After thealumina deposition, no substrate oxides were visible via SEM on thesurface of the specimen. Specimens that only received an alumina coatingshowed, through SEM observation, the presence of substrate oxides grownon the surface.

EXAMPLE 10

Silica was deposited via CCVD processing onto an iron/cobalt alloy,which was easily subject to oxidation, as a base layer for furthersilica deposition at a higher temperature. The initial silica coatingwas deposited at a temperature 100° C. lower than the subsequent silicadeposition. The base layer was deposited along the perimeter of thesubstrate, which was the most susceptible area to oxidation. The baselayer protected the substrate from oxidation during the deposition atthe higher temperature. Specimens without the base layer tended tooxidize during deposition due to the higher, but desired, depositiontemperature.

EXAMPLE 11

A silicon/lead oxide base layer was applied to copper foil before alead/aluminum/boron/silicon oxide coating to protect the substrate fromhigher temperatures it would experience in the subsequent deposition.This higher temperature resulted from either using a higher flametemperature at the surface or from using less auxiliary back coolingthan was used for the base layer deposition.

EXAMPLE 12

Platinum and Gold layers were deposited as follows: wt % Toluene wt %Methanol wt % Propane wt % Isopropyl alcohol Optimum Optimum OptimumOptimum wt % Optimum Component Variation Variation Variation VariationVariation *platinum (II) 0.33 best +/− 19.3 best +/− 80.4 best +/−acetylacetonate 0.14 good 0.05 1.5 good 2 good 2-100 0-98 Diphenyl Pt0.76 best 60.99 38.3 0.38-1.52 50-100 0-49.6 chlorotriethyl 0.3 best +/−59 +/− 1 40.7 +/− 1 phosphine 0.14 good gold (I) chlorotripheny 0.15 +/−15 22.7 +/− 8 77.2 +/− 7 phosphine gold *Note: Pt precursor solution wasprepared as follows: platinum (II) acetylacetonate mixed with toluene,sonicated for several minutes before adding methanol. Two differentkinds of Pt solutions were also used proper to Pt/toluene/methanolsolution. There were 0.3 wt % platinum (II) acetylacetonate mixed with99.7 wt % toluene and 0.3 wt % platinum (II) acetylacetonate mixed with92.6 wt % toluene and 7.1 wt % propane. Among these three solutions,Pt/toluene/methanol solution gave more stable flame, better atomization,and higher quality thin film.

EXAMPLE 13

Chromia Adhesion Improvement layers between dielectrics and electrodesare deposited as follows:

Chromia precursor solution reagent alcohol wt % Toluene wt % 1-butanolwt % Propane wt % 90% ethanol Optimum Optimum Optimum Optimum 10% MeOH +Component Variation Variation Variation Variation isopropyl alcoholchromium (III) 0.15 -1.2 98.8-99.85 2-ethylhexanoate chromium 0.15carbonyl chromium (III) 0.12 14.6 5.7 79.4 acetylacetonate 0.12-0.312-22 2.8-5.7 74-84 Cr 0.91 w/o 14.2 8.5 0.3-1.82 10-50 50-89.7

Among three chromium precursor solutions, chromium (III) acetylacetonatesolution gave best results in terms of thin film microstructure,atomization and solution stability.

EXAMPLE 14

SiO₂ − Pt solution Toulene Methanol isopropyl wt % wt % wt % alcohol wt% Com- Optimum Optimum Optimum Optimum ponent Variation VariationVariation Variation tetraethyl- 0.84 +/− 0.5  16.6 +/− 1.3 77.6 +/− 1.767.62 +/− 2.6 oxysilane COD 0.34 +/− 0.01 platinum (II) acetyl- acetonate

SiO₂—Pt solution was prepared by ultrasonically mixing platinum (II)acetylacetonate, and toluene for several minutes before addition ofmethonal and the tetraethyloxysilane.

EXAMPLE 15

SiCrO_(x) and CrO_(x)Pt precursor solutions isopropyl Toulene 1-butanolPropane component wt % alcohol wt % wt % wt % wt % SiCro_(x)tetraethyloxysilane 0.95 7.87 21.3 4.3 65.2 chromium (III) 0.35acetylacetonate, CrO_(x)Pt chromium(III) 0.17 21.5 8.31 70acetylacetonate platinum (II) 0.023 acetylacetonate

The usable range of each component is 20 percent of variation fromsuggested formula.

EXAMPLE 16

Dielectric materials layers were deposited according to the followingconditions: isopropyl alcohol wt % wt % Toluene wt % Propane wt %Component Optimum Variation Optimum Variation Optimum Variation OptimumVariation Silica tetraethyloxysilane 0.873 7.76 91.4 0.873-1.7  7.76-1288.9-9.92 Lead silicate tetraethyloxysilane 0.496 17.8 17.3 64.40.16-0.72     7-29.1 0.94-29.8  40-92.1 lead naphthenate 0.013 0.01-0.08Electronic glass lead naphthenate 0.36 +/− 0.04 19 +/− 6 23 +/− 9 57 +/−14 tetraethyloxysilane 0.14 +/− 0.13 aluminum 0.06 +/− 0.06acetylacetonate trimethylborate 0.03 +/− 0.03 potassium ethoxide 0.013+/− 0.013 sodium 2,2,6,6- 0.05 +/− 0.05 teramethylheptane- 3,5-dionatelithium t-butoxide 4.5 × 10⁻³ +/− 4.5 × 10⁻³

EXAMPLE 17

BST, LSC, and PLZT precursor solutions wt % Toluene wt % 1-butanolIsopropyl Propane wt % Optimum Optimum Optimum alcohol Optimum ComponentVariation Variation Variation wt % Variation BST barium 0.79 17.4 81.52-ethylhexanoate 0.11-0.83 8-18   80-91.5 strontium 0.142-ethylhexanoate 0.08-0.20 titanium-(di-i- 0.23 propoxide)bis- 0.14-0.30(acetylacetonate) LSC lanthanum 0.21 2.35 6 91.1 2-ethylhexanoate0.09-0.38   2-14.2 0-7.5 85-94 strontium 0.15 2-ethylhexanoate 0.04-0.3 cobalt- 0.1 naphthenate 0.04-0.18 PLZT lead (III) 0.05 0.96 8.6 90.32-ethylhexanoate 0.03-0.18 0.9-12.8 0-10  86.6-92   lanthanum 0.012-ethylhexanoate   0-0.15 zirconium 0.04 n-butoxide 0.035-0.05 titanium-(di-i- 0.035 propoxide)bis- 0.035-0.12  (acetylacetonate)

EXAMPLE 18

PMN, PMY, PbTiO₃, PNZT precursor solutions: Toluene 1-Butanol IsopropylPropane Component wt % wt % wt % alcohol wt % wt % PMN lead naphthenate0.14 15.9 83.8 magnesium 0.04 naphthenate tetrakis(2,2,6,6- 0.12tetramethyt-3,5- heptanedionato)nio bium PMT lead naphthenate 0.12 18.781.1 magnesium 0.02 naphthenate tantalum (V) 0.06 tetraethoxyacetylacetonate PbTiO₃ lead (III) 2- 0.076 7.55 8.58 83.7 ethylhexanoatetitanium-(di-i- propoxide)bis(acet ylacetonate) PNZT lead (III) 2- 0.031.1 8.3 0.12 90.4 ethylhexanoate niobium ethoxide 0.007 zirconium 2-0.01 ethylhexanoate titanium-(di-i- 0.03 propoxide)bis(acet ylacetonate)

The usable range of each component is 20 percent of variation fromsuggested formula for optimization.

EXAMPLE 19

For Strontium Oxide Barrier Layer Deposition

Strontium oxide coatings were deposited onto Cu foil using the CCVDprocess. During the deposition the solution flow rate, oxygen flow rateand cooling air flow rate were kept constant. The solution of thestrontium oxide precursor contained 0.71 wt % strontium2-ethylhexanoate, 12.75 wt % toluene, and 86.54 wt % propane. The flowrate for the solution was 3.0 ml/min and for the oxygen 3500 ml/min at65 psi. The cooling air was at ambient temperature and the flow rate was25 1/min at 80 psi. The cooling air was directed at the back of thesubstrate with a copper tube whose end was positioned 2 inches from theback of the substrate. The deposition was performed at 700° C. flametemperature which was measured at the substrate surface with a Type-Kthermocouple. The cooling air flow rate can be in a range of 15 to 441/min. The deposition temperature can varies from 500 to 800° C.

EXAMPLE 20

For Zinc Oxide Barrier Layer Deposition

Zinc oxide coatings were deposited onto Cu foil using the CCVD process.During the deposition the solution flow rate, oxygen flow rate andcooling air flow rate were kept constant. The solution of the zinc oxideprecursor contained 2.35 wt % zinc 2-ethylhexanoate, 7.79 wt % toluene,and 89.86 wt % propane. The flow rate for the solution was 3.0 ml/minand for the oxygen 4000 ml/min at 65 psi. The cooling air was at ambienttemperature and the flow rate was 25 1/min at 80 psi. The cooling airwas directed at the back of the substrate with a copper tube whose endwas positioned 2 inches from the back of the substrate. The depositionwas performed at 700° C. flame temperature which was measured at thesubstrate surface with a Type-K thermocouple. The cooling air flow ratecan be in a range of 9 to 25 1/min. The deposition temperature canvaries from 625 to 800° C.

EXAMPLE 21

For Tungsten Oxide Barrier Layer Deposition

Tungsten oxide coatings were deposited onto Cu foil using the CCVDprocess. During the deposition the solution flow rate, oxygen flow rateand cooling air flow rate were kept constant. The solution of thetungsten oxide precursor contained 2.06 wt % tungsten hexacarbonyl,26.52 wt % toluene, and 73.28 wt % propane. The flow rate for thesolution was 3.0 ml/min and for the oxygen 3500 ml/min at 65 psi. Nocooling air was used at 350° C. deposition temperature. The temperaturewas measured at the substrate surface with a Type-K thermocouple. Thecooling air flow rate can be introduced in the deposition and directedat the back of the substrate in a range of 7 to 10 l/min. The depositiontemperature can varies from 350 to 800° C.

EXAMPLE 22

SrWO₄ coatings were deposited onto MgO using the CCVD process. Duringthe deposition, the solution flow rate and oxygen flow rate were keptconstant. The solution of the SrWO₄ precursor contained 0.0947 wt % ofSr in the form of Strontium 2-ethylhexanoate, 0.0439 wt % tungstenhexacarbony, 12.7426 wt % toluene, and 86.4855 wt % propane. The flowrate for the solution was 2.0 ml/min and for the oxygen 4000 ml/min at80 psi. The gas temperature was measured at the substrate surface with aType-K thermocouple. The deposition temperature can be varied from 500to 800° C.

EXAMPLE 23

BaWO₄ coatings were deposited onto MgO and Si wafers using the CCVDprocess. During the deposition, the solution flow rate and oxygen flowrate were kept constant. The solution of the BaWO₄ precursor contained0.0855 wt % of Ba in the form of Barium 2-ethylhexanoate, 0.0855 wt %tungsten hexacarbony, 12.4626 wt % toluene, and 84.0336 wt % propane.The flow rate for the solution was 2.0 ml/min and for the oxygen 4000ml/min at 80 psi. The gas temperature was measured at the substratesurface with a Type-K thermocouple. The deposition temperature can bevaried from 500 to 800° C.

EXAMPLE 24

Tungsten oxide coatings were deposited onto Cu foil using the CCVDprocess. During the deposition the solution flow rate, oxygen flow rateand cooling air flow rate were kept constant. The solution of thetungsten oxide precursor contained 2.06 wt % tungsten hexacarbonyl,26.52 wt % toluene, and 73.28 wt % propane. The flow rate for thesolution was 3.0 ml/min and for the oxygen 3500 ml/min at 65 psi. Nocooling air was used at 350° C. deposition temperature. The gastemperature was measured at the substrate surface with a Type-Kthermocouple. The cooling air flow rate can be introduced in thedeposition and directed at the back of the substrate in a range of 7 to10 l/min. The deposition temperature can be varied from 350 to 800° C.

EXAMPLE 25

CeO₂ coatings were deposited onto MgO and Si wafers using the CCVDprocess. During the deposition, the solution flow rate and oxygen flowrate were kept constant. The solution of the CeO₂ precursor contained0.0283 wt % of Ce in the form of Cerium 2-ethylhexanoate, 14.2857 wt %toluene, and 84.0336 wt % propane. The flow rate for the solution was2.0 ml/min and for the oxygen 4000 ml/min at 80 psi. The gas temperaturewas measured at the substrate surface with a Type-K thermocouple. Thedeposition temperature can be varied from 500 to 900° C.

EXAMPLE 26

Strontium oxide coatings were deposited onto Cu foil using the CCVDprocess. During the deposition the solution flow rate, oxygen flow rateand cooling air flow rate were kept constant. The solution of thestrontium oxide precursor contained 0.71 wt % strontium2-ethylhexanoate, 12.75 wt % toluene, and 86.54 wt % propane. The flowrate for the solution was 3.0 ml/min and for the oxygen 3500 ml/min at65 psi. The cooling was at ambient temperature and the flow rate was 25l/min at 80 psi. The cooling air was directed at the back of thesubstrate with a copper tube whose end was positioned 2 inches from theback of the substrate. The deposition was performed at 700° C. flametemperature which was measured at the substrate surface with a Type-Kthermocouple. The cooling air flow rate can be in a range of 15 to 44l/min. The deposition temperature can be varied from 500 to 800° C.

What is claimed is:
 1. A layered structure for acting as or forming atleast one thin layer capacitor comprising in sequence a first metal foilselected from the group consisting of copper, zinc, nickel, iron,niobium, molybdenum, titanium, nickel/chromium alloy,iron/nickel/chromium alloy and aluminum, a dielectric material depositedon the first metal foil and having a thickness of from about 0.03 toabout 2 microns, a second metal layer deposited on the dielectricmaterial, and a barrier layer between about 0.01 and about 0.08 micronsthick between said first metal foil and said dielectric material layer.2. The layered structure according to claim 1 wherein said barrier layeris formed of material selected from the group consisting of tungstenoxide, strontium oxide, and mixed tungsten/strontium oxides.
 3. Thelayered structure according to claim 1 wherein said barrier layer isformed of material selected from the group consisting of BaWO₄, silica,alumina, nickel and platinum.
 4. The layered structure according toclaim 1 wherein said barrier layer is formed of material selected fromthe group consisting of ceria and Sr_(1−x)Ba_(x)WO₄.
 5. The layeredstructure of claim 1 wherein said dielectric material contains betweenabout 1 wt % and about 100 wt % silica.
 6. The layered structure ofclaim 1 wherein said metal foil is selected from the group consisting ofcopper foil, nickel foil and aluminum foil.
 7. The layered structureaccording to claim 1 wherein said foil is between about 12 and about 110microns thick and said second metal layer is between about 0.5 and about3 microns thick.
 8. The layered structure according to claim 1 furthercomprising an adhesion layer between about 0.0001 and about 0.05 micronsthick between said dielectric material layer and said second metallayer.
 9. The layered structure according to claim 1 wherein saiddielectric material layer is selected from the group consisting of BST,SrTiO₃, Ta_(2l O) ₅, TiO₂, MnO₂, Y₂O₃, SnO₂, and PLZT.
 10. The layeredstructure according to claim 1 wherein said dielectric material layer isselected from the group consisting of barium titanium oxide,zirconium-doped barium titanium oxide, and tin-doped barium titaniumoxide.
 11. The layered structure according to claim 1 wherein saiddielectric material layer is selected from the group consisting of WO₃,SrO, mixed tungsten strontium oxides, BaWO₄, CeO₂, andSr_(1−x)Ba_(x)WO₄.
 12. The layered structure in accordance with claim 1wherein said first metal foil has a surface roughness on the side ofsaid dielectric material layer of at least about 1.1 cm²/cm².
 13. Alayered structure for acting as or forming at least one thin layercapacitor comprising in sequence a first metal foil selected from thegroup consisting of copper, zinc, nickel, iron, niobium, molybdenum,titanium, nickel/chromium alloy, iron/nickel/chromium alloy andaluminum, a dielectric material deposited on the first metal foil andhaving a thickness of from about 0.03 to about 2 microns, a second metallayer deposited on the dielectric material, and an adhesion layerbetween about 0.0001 and about 0.05 microns thick between saiddielectric material layer and said second metal layer.
 14. The layeredstructure according to claim 13 wherein said adhesion layer is afunctionally gradient material.
 15. The layered structure of claim 13wherein said dielectric material contains between about 1 wt % and about100 wt % silica.
 16. The layered structure of claim 13 wherein saidmetal foil is selected from the group consisting of copper foil, nickelfoil and aluminum foil.
 17. The layered structure according to claim 13wherein said foil is between about 12 and about 110 microns thick andsaid second metal layer is between about 0.5 and about 3 microns thick.18. The layered structure according to claim 13 wherein said first metalfoil is a coating between about 0.5 and about 3 microns thick on apolymeric support sheet.
 19. The layered structure according to claim 13wherein said dielectric material layer is selected from the groupconsisting of BST, SrTiO₃, Ta₂O₅, TiO₂, MnO₂, Y₂O₃, SnO₂, and PLZT. 20.The layered structure according to claim 13 wherein said dielectricmaterial layer is selected from the group consisting of barium titaniumoxide, zirconium-doped barium titanium oxide, and tin-doped bariumtitanium oxide.
 21. The layered structure according to claim 13 whereinsaid dielectric material layer is selected from the group consisting ofWO₃, SrO, mixed tungsten strontium oxides, BaWO₄, CeO₂, andSr_(1−x)Ba_(x)WO₄.
 22. A layered structure for acting as or forming atleast one thin layer capacitor comprising in sequence a first metal foilselected from the group consisting of copper, zinc, nickel, iron,niobium, molybdenum, titanium, nickel/chromium alloy,iron/nickel/chromium alloy and aluminum, a dielectric material depositedon the first metal foil and having a thickness of from about 0.03 toabout 2 microns, and a second metal layer deposited on the dielectricmaterial, said dielectric material layer being chemically doped to belossy having an electrical conductivity value of from about 10⁻¹ toabout 10⁻⁵ amperes per cm².
 23. The layered structure of claim 22wherein said dielectric material contains between about 1 wt % and about100 wt % silica.
 24. The layered structure of claim 22 wherein saidfirst metal foil is selected from the group consisting of copper foil,nickel foil and aluminum foil.
 25. The layered structure according toclaim 22 wherein said foil is between about 12 and about 110 micronsthick and said second metal layer is between about 0.5 and about 3microns thick.
 26. The layered structure according to claim 22 whereinsaid first metal foil is a coating between about 0.5 and about 3 micronsthick on a polymeric support sheet.
 27. The layered structure accordingto claim 22 further comprising an adhesion layer between about 0.0001and about 0.05 microns thick between said dielectric material layer andsaid second metal layer.
 28. The layered structure according to claim 22wherein said dielectric material layer is selected from the groupconsisting of BST, SrTiO₃, Ta₂O₅, TiO₂, MnO₂, Y₂O₃, SnO₂, and PLZT. 29.The layered structure according to claim 22 further comprising a barrierlayer between about 0.01 and about 0.08 microns thick between said firstmetal foil and said dielectric material layer.